diff --git a/docs/_static/custom.css b/docs/_static/custom.css
index 76574a6..2909810 100644
--- a/docs/_static/custom.css
+++ b/docs/_static/custom.css
@@ -1,3 +1,11 @@
 .wy-nav-content {
     max-width: 100% !important;
 }
+
+
+/* To change the left bar of executable cells in markdown and executable cells in jupyter notebooks */
+/* See https://github.com/executablebooks/meta/discussions/667 */
+div.cell div.cell_input {
+    border-left-color: #343131;
+}
+
diff --git a/docs/contents/about/showcase/Quick_Guide.ipynb b/docs/contents/about/showcase/Quick_Guide.ipynb
index 30b8e5a..1cfcaf9 100644
--- a/docs/contents/about/showcase/Quick_Guide.ipynb
+++ b/docs/contents/about/showcase/Quick_Guide.ipynb
@@ -68,6 +68,26 @@
     "puw.configure.get_default_form()"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "'pint'"
+      ]
+     },
+     "execution_count": 5,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "puw.configure.get_default_parser()"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -79,7 +99,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": 6,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -88,7 +108,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 6,
+   "execution_count": 7,
    "metadata": {},
    "outputs": [
     {
@@ -103,7 +123,7 @@
        "2.5 <Unit('nanometer / picosecond')>"
       ]
      },
-     "execution_count": 6,
+     "execution_count": 7,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -121,7 +141,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 7,
+   "execution_count": 8,
    "metadata": {},
    "outputs": [
     {
@@ -130,7 +150,7 @@
        "True"
       ]
      },
-     "execution_count": 7,
+     "execution_count": 8,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -141,7 +161,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 8,
+   "execution_count": 9,
    "metadata": {},
    "outputs": [
     {
@@ -150,7 +170,7 @@
        "'pint'"
       ]
      },
-     "execution_count": 8,
+     "execution_count": 9,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -168,7 +188,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 9,
+   "execution_count": 10,
    "metadata": {},
    "outputs": [
     {
@@ -177,7 +197,7 @@
        "2.5"
       ]
      },
-     "execution_count": 9,
+     "execution_count": 10,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -188,7 +208,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 10,
+   "execution_count": 11,
    "metadata": {},
    "outputs": [
     {
@@ -203,7 +223,7 @@
        "<Unit('nanometer / picosecond')>"
       ]
      },
-     "execution_count": 10,
+     "execution_count": 11,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -221,7 +241,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 11,
+   "execution_count": 12,
    "metadata": {},
    "outputs": [
     {
@@ -230,7 +250,7 @@
        "{'[L]': 1, '[M]': 0, '[T]': -1, '[K]': 0, '[mol]': 0, '[A]': 0, '[Cd]': 0}"
       ]
      },
-     "execution_count": 11,
+     "execution_count": 12,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -248,7 +268,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 12,
+   "execution_count": 13,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -257,7 +277,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 13,
+   "execution_count": 14,
    "metadata": {},
    "outputs": [
     {
@@ -266,7 +286,7 @@
        "'openmm.unit'"
       ]
      },
-     "execution_count": 13,
+     "execution_count": 14,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -277,7 +297,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 14,
+   "execution_count": 15,
    "metadata": {},
    "outputs": [
     {
@@ -286,7 +306,7 @@
        "Quantity(value=2.5, unit=nanometer/picosecond)"
       ]
      },
-     "execution_count": 14,
+     "execution_count": 15,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -304,7 +324,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 15,
+   "execution_count": 16,
    "metadata": {},
    "outputs": [
     {
@@ -329,7 +349,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 16,
+   "execution_count": 17,
    "metadata": {},
    "outputs": [
     {
@@ -338,7 +358,7 @@
        "{'[L]': 1.0, '[M]': 0, '[T]': -1.0, '[K]': 0, '[mol]': 0, '[A]': 0, '[Cd]': 0}"
       ]
      },
-     "execution_count": 16,
+     "execution_count": 17,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -356,7 +376,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 17,
+   "execution_count": 18,
    "metadata": {},
    "outputs": [
     {
@@ -365,7 +385,7 @@
        "True"
       ]
      },
-     "execution_count": 17,
+     "execution_count": 18,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -383,7 +403,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 18,
+   "execution_count": 19,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -392,7 +412,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 19,
+   "execution_count": 20,
    "metadata": {},
    "outputs": [
     {
@@ -401,7 +421,7 @@
        "Unit({BaseUnit(base_dim=BaseDimension(\"amount\"), name=\"mole\", symbol=\"mol\"): -1.0, ScaledUnit(factor=1000.0, master=meter*newton, name='kilojoule', symbol='kJ'): 1.0})"
       ]
      },
-     "execution_count": 19,
+     "execution_count": 20,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -419,7 +439,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 20,
+   "execution_count": 21,
    "metadata": {},
    "outputs": [
     {
@@ -428,7 +448,7 @@
        "'openmm.unit'"
       ]
      },
-     "execution_count": 20,
+     "execution_count": 21,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -439,7 +459,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 21,
+   "execution_count": 22,
    "metadata": {},
    "outputs": [
     {
@@ -448,7 +468,7 @@
        "True"
       ]
      },
-     "execution_count": 21,
+     "execution_count": 22,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -466,7 +486,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 22,
+   "execution_count": 23,
    "metadata": {},
    "outputs": [
     {
@@ -481,7 +501,7 @@
        " '[Cd]': 0}"
       ]
      },
-     "execution_count": 22,
+     "execution_count": 23,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -499,7 +519,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 23,
+   "execution_count": 24,
    "metadata": {},
    "outputs": [
     {
@@ -508,7 +528,7 @@
        "'kilojoule/mole'"
       ]
      },
-     "execution_count": 23,
+     "execution_count": 24,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -526,7 +546,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 24,
+   "execution_count": 25,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -535,7 +555,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 25,
+   "execution_count": 26,
    "metadata": {},
    "outputs": [
     {
@@ -544,7 +564,7 @@
        "Quantity(value=1.75, unit=newton/(nanometer**2))"
       ]
      },
-     "execution_count": 25,
+     "execution_count": 26,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -562,7 +582,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 26,
+   "execution_count": 27,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -571,7 +591,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 27,
+   "execution_count": 28,
    "metadata": {},
    "outputs": [
     {
@@ -586,7 +606,7 @@
        "array([0., 0., 0.]) <Unit('nanometer')>"
       ]
      },
-     "execution_count": 27,
+     "execution_count": 28,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -604,7 +624,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 28,
+   "execution_count": 29,
    "metadata": {},
    "outputs": [
     {
@@ -613,7 +633,7 @@
        "'[0.0 0.0 0.0] nanometer'"
       ]
      },
-     "execution_count": 28,
+     "execution_count": 29,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -631,7 +651,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 29,
+   "execution_count": 30,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -640,7 +660,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 30,
+   "execution_count": 31,
    "metadata": {},
    "outputs": [
     {
@@ -655,7 +675,7 @@
        "<Unit('kelvin')>"
       ]
      },
-     "execution_count": 30,
+     "execution_count": 31,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -666,7 +686,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 31,
+   "execution_count": 32,
    "metadata": {},
    "outputs": [
     {
@@ -675,7 +695,7 @@
        "'kelvin'"
       ]
      },
-     "execution_count": 31,
+     "execution_count": 32,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -700,7 +720,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 32,
+   "execution_count": 33,
    "metadata": {},
    "outputs": [
     {
@@ -709,7 +729,7 @@
        "['pint', 'openmm.unit']"
       ]
      },
-     "execution_count": 32,
+     "execution_count": 33,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -720,7 +740,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 33,
+   "execution_count": 34,
    "metadata": {},
    "outputs": [
     {
@@ -729,7 +749,7 @@
        "'pint'"
       ]
      },
-     "execution_count": 33,
+     "execution_count": 34,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -747,7 +767,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 34,
+   "execution_count": 35,
    "metadata": {},
    "outputs": [
     {
@@ -776,7 +796,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 35,
+   "execution_count": 36,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -785,7 +805,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 36,
+   "execution_count": 37,
    "metadata": {},
    "outputs": [
     {
@@ -817,7 +837,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 37,
+   "execution_count": 38,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -834,7 +854,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 38,
+   "execution_count": 39,
    "metadata": {},
    "outputs": [
     {
@@ -870,7 +890,7 @@
        "  '[Cd]': 0}}"
       ]
      },
-     "execution_count": 38,
+     "execution_count": 39,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -881,7 +901,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 39,
+   "execution_count": 40,
    "metadata": {},
    "outputs": [
     {
@@ -890,7 +910,7 @@
        "'pint'"
       ]
      },
-     "execution_count": 39,
+     "execution_count": 40,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -908,7 +928,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 40,
+   "execution_count": 41,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -917,7 +937,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 41,
+   "execution_count": 42,
    "metadata": {},
    "outputs": [
     {
@@ -942,7 +962,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 42,
+   "execution_count": 43,
    "metadata": {},
    "outputs": [
     {
@@ -967,7 +987,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 43,
+   "execution_count": 44,
    "metadata": {},
    "outputs": [
     {
@@ -990,15 +1010,6 @@
     "As you noticed, we have mention that `pyunitwizard.get_standard` and `pyunitwizard.standardize` results with the compatible default standard units. This is combination of standard units are also considered:"
    ]
   },
-  {
-   "cell_type": "code",
-   "execution_count": 44,
-   "metadata": {},
-   "outputs": [],
-   "source": [
-    "q = puw.quantity('100 angstroms**3')"
-   ]
-  },
   {
    "cell_type": "code",
    "execution_count": 45,
@@ -1105,7 +1116,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.7.10"
+   "version": "3.7.12"
   }
  },
  "nbformat": 4,
diff --git a/pyunitwizard/_private_tools/exceptions.py b/pyunitwizard/_private_tools/exceptions.py
index c40ed24..db1d617 100644
--- a/pyunitwizard/_private_tools/exceptions.py
+++ b/pyunitwizard/_private_tools/exceptions.py
@@ -18,7 +18,7 @@ class NotImplementedMethodError(NotImplementedError):
 
     Examples
     --------
-    >>> from pyuniwizard._private_tools.exceptions import NotImplementedMethodError
+    >>> from pyunitwizard._private_tools.exceptions import NotImplementedMethodError
     >>> def method_name(a, b=True):
     ...    raise NotImplementedMethodError
     ...    pass
@@ -32,7 +32,7 @@ class NotImplementedMethodError(NotImplementedError):
 
     def __init__(self):
 
-        from pyuniwizard import __github_issues_web__
+        from pyunitwizard import __github_issues_web__
         from inspect import stack
 
         all_stack_frames = stack()
@@ -70,7 +70,7 @@ class NotImplementedClassError(NotImplementedError):
 
     Examples
     --------
-    >>> from pyuniwizard._private_tools.exceptions import NotImplementedClassError
+    >>> from pyunitwizard._private_tools.exceptions import NotImplementedClassError
     >>> class ClassName():
     ...    def __init__(self):
     ...       raise NotImplementedClassError
@@ -85,7 +85,7 @@ class NotImplementedClassError(NotImplementedError):
 
     def __init__(self):
 
-        from pyuniwizard import __github_issues_web__
+        from pyunitwizard import __github_issues_web__
         from inspect import stack
 
         all_stack_frames = stack()
@@ -102,6 +102,57 @@ def __init__(self):
 
         super().__init__(message)
 
+
+class NotImplementedParsingError(NotImplementedError):
+    """Exception raised when parsing a string with the parser and to the form choosen has not been
+    implemented yet.
+
+    This exception is raised when parsing a strint with the parser and to the form choosen by the
+    user, has not been implemented yet.
+
+    Parameters
+    ----------
+    parser : str
+        The name of the parser choosen by the user.
+    to_form : str
+        The name of target form choosen by the user.
+
+    Raises
+    ------
+    NotImplementedMethodError
+        A message is printed out with the link to the documentation section about parsing strings,
+        and the link to the issues board of PyUnitWizard's GitHub repository.
+
+    Examples
+    --------
+    >>> from pyunitwizard._private_tools.exceptions import NotImplementedParsingError
+    >>> def method_name(string, parser='pint', to_form='new_form'):
+    ...    if parser=='pint' and to_form='new_form':
+    ...       raise NotImplementedParsingError('pint', 'new_form')
+    ...    pass
+
+    .. admonition:: See Also
+       :class: attention
+
+        :ref:`Developer Guide \> Exceptions \> NotImplementedParsingError <developer:exceptions:NotImplementedParsingError>`
+
+    """
+
+    def __init__(self, parser, to_form):
+
+        from pyunitwizard import __github_issues_web__
+
+        api_doc = ''
+
+        message = (
+                f"Parsing a string with the \"{parser}\" parser to the form \"{to_form}\" has not been implemented yet. "
+                f"Check {api_doc} for more information. "
+                f"If you still want to suggest its implementation, open a new issue in {__github_issues_web__}"
+                )
+
+        super().__init__(message)
+
+
 class BadCallError(ValueError):
     """Exception raised when a method, or a class, was not properly called or instantiated.
 
@@ -121,7 +172,7 @@ class BadCallError(ValueError):
 
     Examples
     --------
-    >>> from pyuniwizard._private_tools.exceptions import BadCallError
+    >>> from pyunitwizard._private_tools.exceptions import BadCallError
     >>> def method_name(item, a=True):
     ...    if type(a) not in [int, float]:
     ...       raise BadCallError('a')
@@ -136,7 +187,7 @@ class BadCallError(ValueError):
 
     def __init__(self, argument=None):
 
-        from pyuniwizard import __github_issues_web__
+        from pyunitwizard import __github_issues_web__
         from inspect import stack
 
         all_stack_frames = stack()
@@ -186,7 +237,7 @@ class NoStandardError(ValueError):
 
     def __init__(self):
 
-        from pyuniwizard import __github_issues_web__
+        from pyunitwizard import __github_issues_web__
         from inspect import stack
 
         all_stack_frames = stack()
@@ -313,5 +364,62 @@ def __init__(self, library):
 
         super().__init__(message)
 
+class LibraryWithoutParserError(NotImplementedError):
+    """Exception raised when a library can not parse strings.
+
+    Some libraries cannot convert strings to quantities. This error will be raised by the API methods
+    `string_to_quantity` and `string_to_unit` of those libraries without strings' parser.
+
+    Parameters
+    ----------
+    argument : str
+        The name of the library without parser.
+
+    Raises
+    ------
+    LibraryWithoutParserError
+        A message is printed out with the name of the library wihtout parser, the link to the
+        section in the documentation regarding parser regarding parsers, and the link to the
+        issues board of PytUnitWizard's GitHub repository.
+
+    Examples
+    --------
+    >>> import pyunitwizard as puw
+    >>> from pyunitwizard._private_tools.exceptions import LibraryWithoutParserError
+    >>> from pyunitwizard._private_tools.exceptions import LibraryWithoutParserError
+    >>> def method_name(item, argument='pint'):
+    ...    if argument == 'pint':
+    ...       try:
+    ...          import pint
+    ...       except:
+    ...          raise LibraryNotFoundError('pint')
+    ...    pass
+
+    .. admonition:: See Also
+       :class: attention
+
+        :ref:`Developer Guide \> Exceptions \> LibraryWithoutStringsParserError <developer:exceptions:LibraryWithoutStringsParserError>`
+
+    """
+
+    def __init__(self, library):
+
+        from pyunitwizard import __github_issues_web__
+        from inspect import stack
+
+        all_stack_frames = stack()
+        caller_stack_frame = all_stack_frames[1]
+        caller_name = caller_stack_frame[3]
+
+        api_doc = ''
+
+        message = (
+                f"The python library {library} was not found. "
+                f"Although {library} is not considered a dependency, it needs "
+                f"to be installed to execute the {caller_name} method the way you require. "
+                f"If you still need help, open a new issue in {__github_issues_web__}."
+                )
+
+        super().__init__(message)
 
 
diff --git a/pyunitwizard/_private_tools/forms.py b/pyunitwizard/_private_tools/forms.py
index 09ef6c2..bbc9ef0 100644
--- a/pyunitwizard/_private_tools/forms.py
+++ b/pyunitwizard/_private_tools/forms.py
@@ -17,12 +17,16 @@ def digest_form(form):
 
     return output
 
-def digest_to_form(to_form):
+def digest_to_form(to_form, from_form=None):
 
     output = None
 
     if to_form is not None:
         output = digest_form(to_form)
+    else:
+        if from_form == 'string':
+            from_form = None
+        output = digest_form(from_form)
 
     return output
 
diff --git a/pyunitwizard/_private_tools/parsers.py b/pyunitwizard/_private_tools/parsers.py
index 1f74d81..8a48c74 100644
--- a/pyunitwizard/_private_tools/parsers.py
+++ b/pyunitwizard/_private_tools/parsers.py
@@ -9,6 +9,9 @@ def digest_parser(parser):
             output = parser.lower()
         else:
             raise ValueError
+    else:
+        from pyunitwizard.kernel import default_parser
+        output = default_parser
 
     return output
 
diff --git a/pyunitwizard/forms/__init__.py b/pyunitwizard/forms/__init__.py
index 6652af2..b6cff57 100644
--- a/pyunitwizard/forms/__init__.py
+++ b/pyunitwizard/forms/__init__.py
@@ -9,7 +9,6 @@
 dict_translate={}
 dict_convert={}
 dict_string_to_quantity={}
-dict_string_to_unit={}
 dict_to_string={}
 dict_dimensionality={}
 dict_compatibility={}
@@ -32,7 +31,7 @@ def load_library(library):
     dict_convert[library] = api.convert
     dict_translate[library]={}
     dict_string_to_quantity[library] = api.string_to_quantity
-    dict_string_to_unit[library] = api.string_to_unit
+    dict_to_string[library] = api.to_string
     dict_dimensionality[library] = api.dimensionality
     dict_compatibility[library] = api.compatibility
 
@@ -76,7 +75,7 @@ def load_library(library):
 dict_convert['string'] = api.convert
 dict_translate['string']={}
 dict_string_to_quantity['string'] = api.string_to_quantity
-dict_string_to_unit['string'] = api.string_to_unit
+dict_to_string['string'] = api.to_string
 dict_dimensionality['string'] = api.dimensionality
 dict_compatibility['string'] = api.compatibility
 
diff --git a/pyunitwizard/forms/api_openmm_unit.py b/pyunitwizard/forms/api_openmm_unit.py
index 2bddac1..5c60bb5 100644
--- a/pyunitwizard/forms/api_openmm_unit.py
+++ b/pyunitwizard/forms/api_openmm_unit.py
@@ -13,12 +13,6 @@
     openmm_unit.Unit:form_name,
     }
 
-try:
-    from pint.util import ParserHelper as PintParserHelper
-    from .api_pint import string_to_quantity as string_to_pint_quantity
-except:
-    PintParserHelper=None
-
 def is_quantity(quantity_or_unit):
 
     output = (type(quantity_or_unit)==openmm_unit.Quantity)
@@ -77,36 +71,20 @@ def compatibility(quantity_or_unit_1, quantity_or_unit_2):
     return tmp_unit_1.is_compatible(tmp_unit_2)
 
 
-def make_quantity(value, unit_name):
+def make_quantity(value, unit):
 
-    unit=string_to_unit(unit_name)
     return openmm_unit.Quantity(value, unit)
 
 def string_to_quantity(string):
 
-    if PintParserHelper is None:
-        raise PintNotFoundError()
-
-    pint_quantity = string_to_pint_quantity(string)
-    parser = PintParserHelper.from_string(pint_quantity.__str__())
-    tmp_quantity = parser.scale
-    for unit_name, exponent in parser.items():
-        tmp_quantity *= getattr(openmm_unit, unit_name)**exponent
-    return tmp_quantity
-
-def string_to_unit(string):
-
-    tmp_quantity = string_to_quantity(string)
-    tmp_unit = get_unit(tmp_quantity)
-    return tmp_unit
+    raise LibraryWithoutStringsParserError('openmm.unit')
 
 def to_string(quantity_or_unit):
 
     return quantity_or_unit.__str__()
 
-def convert(quantity, unit_name):
+def convert(quantity, unit):
 
-    unit = string_to_unit(unit_name)
     return quantity.in_units_of(unit)
 
 def get_value(quantity):
diff --git a/pyunitwizard/forms/api_pint.py b/pyunitwizard/forms/api_pint.py
index c427e47..8b289c6 100644
--- a/pyunitwizard/forms/api_pint.py
+++ b/pyunitwizard/forms/api_pint.py
@@ -84,26 +84,7 @@ def get_unit(quantity):
 
 def string_to_quantity(string):
 
-    if string.startswith('[') or string.startswith('('):
-
-        import ast
-
-        end_list = max(string.rfind(')')+1, string.rfind(']')+1)
-        value_string = string[:end_list]
-        unit_string = string[end_list:]
-
-        tmp_quantity=ast.literal_eval(value_string)*Q_(unit_string)
-
-    else:
-
-        tmp_quantity=Q_(string)
-
-    return tmp_quantity
-
-def string_to_unit(string):
-
-    tmp_quantity = string_to_quantity(string)
-    return get_unit(tmp_quantity)
+    return Q_(string)
 
 def to_string(quantity_or_item):
 
@@ -115,12 +96,20 @@ def convert(quantity, unit_name):
 
 def to_openmm_unit(quantity):
 
-    from .api_openmm_unit import make_quantity as make_openmm_unit_quantity
+    from pint.util import ParserHelper as PintParserHelper
+    try:
+        import openmm.unit as openmm_unit
+    except:
+        raise LibraryNotFoundError('openmm')
 
-    value = get_value(quantity)
-    unit_name = to_string(get_unit(quantity))
+    pint_parser = PintParserHelper.from_string(quantity.__str__())
+    tmp_quantity = pint_parser.scale
+    for unit_name, exponent in pint_parser.items():
+        if unit_name in ['unified_atomic_mass_unit']:
+            unit_name = 'amu'
+        tmp_quantity *= getattr(openmm_unit, unit_name)**exponent
 
-    return make_openmm_unit_quantity(value, unit_name)
+    return tmp_quantity
 
 def to_unyt(quantity):
 
diff --git a/pyunitwizard/forms/api_string.py b/pyunitwizard/forms/api_string.py
index e8b270b..764da09 100644
--- a/pyunitwizard/forms/api_string.py
+++ b/pyunitwizard/forms/api_string.py
@@ -29,10 +29,10 @@ def is_unit(quantity_or_unit):
 def dimensionality(quantity_or_unit):
 
     from pyunitwizard.kernel import default_form, default_parser
-    from pyunitwizard import convert as _convert, dimensionality as _dimensionality
+    from pyunitwizard import convert as _convert, get_dimensionality as _get_dimensionality
 
     tmp_quantity_or_unit = _convert(quantity_or_unit, to_form=default_form, parser=default_parser)
-    output = _dimensionality(tmp_quantity_or_unit)
+    output = _get_dimensionality(tmp_quantity_or_unit)
 
     return output
 
@@ -70,11 +70,12 @@ def get_value(quantity):
 
 def get_unit(quantity):
 
-    from pyunitwizard.kernel import default_form, default_parser
+    from pyunitwizard.kernel import default_parser
     from pyunitwizard import convert as _convert, get_unit as _get_unit
 
-    tmp_quantity_or_unit = _convert(quantity, to_form=default_form, parser=default_parser)
-    tmp_unit = _get_unit(tmp_quantity_or_unit, to_form='string', parser=default_parser)
+    tmp_quantity_or_unit = _convert(quantity, to_form=default_parser)
+    tmp_unit = _get_unit(tmp_quantity_or_unit)
+    tmp_unit = _convert(tmp_unit, to_form='string')
 
     return tmp_unit
 
@@ -82,11 +83,6 @@ def string_to_quantity(string):
 
     return string
 
-def string_to_unit(string):
-
-    tmp_quantity = string_to_quantity(string)
-    return get_unit(tmp_quantity)
-
 def to_string(quantity_or_item):
 
     return quantity_or_item
@@ -97,7 +93,7 @@ def convert(quantity, unit_name):
     from pyunitwizard import convert as _convert, get_unit as _get_unit
 
     tmp_quantity_or_unit = _convert(quantity, to_form=default_form, parser=default_parser)
-    tmp_quantity_or_unit = _convert(tmp_quantity_or_unit, to_units=unit_name, parser=default_parser)
+    tmp_quantity_or_unit = _convert(tmp_quantity_or_unit, to_unit=unit_name, parser=default_parser)
     tmp_quantity_or_unit = _convert(tmp_quantity_or_unit, to_form='string')
 
     return tmp_quantity_or_unit
diff --git a/pyunitwizard/forms/api_unyt.py b/pyunitwizard/forms/api_unyt.py
index ec7140b..c4a25ed 100644
--- a/pyunitwizard/forms/api_unyt.py
+++ b/pyunitwizard/forms/api_unyt.py
@@ -44,10 +44,6 @@ def string_to_quantity(string):
 
     raise NotImplementedMethodError()
 
-def string_to_unit(string):
-
-    raise NotImplementedMethodError()
-
 def to_string(unit):
 
     raise NotImplementedMethodError()
diff --git a/pyunitwizard/forms/template_api_form.py b/pyunitwizard/forms/template_api_form.py
index 54973cf..5880229 100644
--- a/pyunitwizard/forms/template_api_form.py
+++ b/pyunitwizard/forms/template_api_form.py
@@ -30,10 +30,6 @@ def string_to_quantity(string):
 
     raise NotImplementedError
 
-def string_to_unit(string):
-
-    raise NotImplementedError
-
 def to_string(unit):
 
     raise NotImplementedError
diff --git a/pyunitwizard/main.py b/pyunitwizard/main.py
index 266dbab..2f4a83e 100644
--- a/pyunitwizard/main.py
+++ b/pyunitwizard/main.py
@@ -3,8 +3,9 @@
 from ._private_tools.parsers import digest_parser
 from .forms import dict_is_form, dict_is_unit, dict_is_quantity, dict_dimensionality, dict_compatibility
 from .forms import dict_get_unit, dict_get_value, dict_make_quantity
-from .forms import dict_convert, dict_translate, dict_string_to_quantity, dict_string_to_unit, dict_to_string
+from .forms import dict_convert, dict_translate, dict_to_string
 from .import kernel
+from .parse import parse as _parse
 import numpy as np
 
 def get_form(quantity_or_unit):
@@ -184,179 +185,95 @@ def quantity(value, unit=None, form=None, parser=None):
 
     return output
 
-def unit(unit_name, form=None, parser=None):
+def unit(unit, form=None, parser=None):
 
-    return convert(unit_name, to_form=form, parser=parser, to_type='unit')
+    return convert(unit, to_form=form, parser=parser, to_type='unit')
 
 def convert(quantity_or_unit, to_unit=None, to_form=None, parser=None, to_type='quantity'):
 
     output = None
 
     form_in = get_form(quantity_or_unit)
-    to_form = digest_to_form(to_form)
+    to_form = digest_to_form(to_form, form_in)
     parser = digest_parser(parser)
 
-    if to_form is None:
-        if form_in == 'string':
-            to_form=kernel.default_form
-        else:
-            to_form=form_in
-
-    if parser is None:
-        if form_in == 'string':
-            if to_form == 'string':
-                parser = kernel.default_parser
-            else:
-                parser = to_form
-        else:
-            if to_form is None:
-                parser = kernel.default_parser
-            else:
-                parser = form_in
+    if to_type not in ['unit', 'value', 'quantity']:
+        raise BadCallError("to_type")
 
-    output = quantity_or_unit
+    if type(to_unit) is str:
+        to_unit = _parse(to_unit, parser=parser, to_form=to_form)
+        to_unit = dict_get_unit[to_form](to_unit)
 
-    if to_type=='quantity':
+    if form_in=='string':
 
-        if form_in=='string':
-            if parser==to_form:
-                output = dict_translate[form_in][to_form](output)
-                if to_unit is not None:
-                    output = dict_convert[to_form](output, to_unit)
-            else:
-                output = dict_translate[form_in][parser](output)
-                if to_unit is not None:
-                    output = dict_convert[parser](output, to_unit)
-                output = dict_translate[parser][to_form](output)
-        else:
-            if form_in==to_form:
-                if to_unit is not None:
-                    if parser==to_form:
-                        output = dict_convert[form_in](output, to_unit)
-                    else:
-                        output = dict_translate[form_in][parser](output)
-                        output = dict_convert[parser](output, to_unit)
-                        output = dict_translate[parser][to_form](output)
-            elif form_in!=to_form:
-                if to_unit is not None:
-                    if parser==form_in:
-                        output = dict_convert[form_in](output, to_unit)
-                        output = dict_translate[form_in][to_form](output)
-                    elif parser==to_form:
-                        output = dict_translate[form_in][to_form](output)
-                        output = dict_convert[to_form](output, to_unit)
-                    else:
-                        output = dict_translate[form_in][parser](output)
-                        output = dict_convert[parser](output, to_unit)
-                        output = dict_translate[parser][to_form](output)
-                else:
-                    output = dict_translate[form_in][to_form](output)
+        if to_form=='string':
 
-    elif to_type=='unit':
+            output = _parse(quantity_or_unit, parser=parser, to_form=parser)
 
-        if form_in=='string':
-            if parser==to_form:
-                if to_unit is None:
-                    output = dict_string_to_unit[to_form](output)
+            if to_unit is not None:
+                output = dict_convert[parser](output, to_unit)
+            if to_type == 'unit':
+                if is_unit(output):
+                    output=output
                 else:
-                    output = dict_string_to_quantity[to_form](output)
-                    output = dict_convert[to_form](output, to_unit)
-                    output = dict_get_unit[to_form](output)
-            else:
-                if to_unit is None:
-                    output = dict_translate[form_in][parser](output)
                     output = dict_get_unit[parser](output)
-                    output = dict_translate[parser][to_form](output)
-                else:
-                    output = dict_translate[form_in][parser](output)
-                    output = dict_convert[parser](output, to_unit)
-                    output = dict_get_unit[parser](output)
-                    output = dict_translate[parser][to_form](output)
+                output = dict_to_string[parser](output)
+            elif to_type == 'value':
+                output = dict_get_value[parser](output)
+                output = str(output)
+            else:
+                output = dict_to_string[parser](output)
+
         else:
-            if form_in==to_form:
-                if to_unit is not None:
-                    if parser==to_form:
-                        output = dict_convert[form_in](output, to_unit)
-                    else:
-                        output = dict_translate[form_in][parser](output)
-                        output = dict_convert[parser](output, to_unit)
-                        output = dict_translate[parser][to_form](output)
-                output = dict_get_unit[to_form](output)
-            elif form_in!=to_form:
-                if to_form == 'string':
-                    if to_unit is not None:
-                        if parser==form_in:
-                            output = dict_convert[form_in](output, to_unit)
-                            output = dict_get_unit[form_in](output)
-                            output = dict_translate[form_in][to_form](output)
-                        else:
-                            output = dict_translate[form_in][parser](output)
-                            output = dict_convert[parser](output, to_unit)
-                            output = dict_get_unit[parser](output)
-                            output = dict_translate[parser][to_form](output)
-                    else:
-                        output = dict_get_unit[form_in](output)
-                        output = dict_translate[form_in][to_form](output)
+
+            output = _parse(quantity_or_unit, parser=parser, to_form=to_form)
+
+            if to_unit is not None:
+                output = dict_convert[to_form](output, to_unit)
+            if to_type == 'unit':
+                if is_unit(output):
+                    output=output
                 else:
-                    if to_unit is not None:
-                        if parser==form_in:
-                            output = dict_convert[form_in](output, to_unit)
-                            output = dict_translate[form_in][to_form](output)
-                        elif parser==to_form:
-                            output = dict_translate[form_in][to_form](output)
-                            output = dict_convert[to_form](output, to_unit)
-                        else:
-                            output = dict_translate[form_in][parser](output)
-                            output = dict_convert[parser](output, to_unit)
-                            output = dict_translate[parser][to_form](output)
-                    else:
-                        output = dict_translate[form_in][to_form](output)
                     output = dict_get_unit[to_form](output)
+            elif to_type == 'value':
+                output = dict_get_value[to_form](output)
 
-    elif to_type=='value':
+    else:
 
-        if form_in=='string':
-            if parser==to_form:
-                output = dict_string_to_quantity[to_form](output)
-                if to_unit is not None:
-                    output = dict_convert[to_form](output, to_unit)
-                output = dict_get_value[to_form](output)
+        if to_form=='string':
+
+            output = quantity_or_unit
+
+            if to_unit is not None:
+                output = dict_convert[form_in](output, to_unit)
+            if to_type == 'unit':
+                if is_unit(output):
+                    output=output
+                else:
+                    output = dict_get_unit[form_in](output)
+                output = dict_to_string[form_in](output)
+            elif to_type == 'value':
+                output = dict_get_value[form_in](output)
+                output = str(output)
             else:
-                output = dict_translate[form_in][parser](output)
-                if to_unit is not None:
-                    output = dict_convert[parser](output, to_unit)
-                output = dict_get_value[parser](output)
+                output = dict_to_string[form_in](output)
+
         else:
-            if form_in==to_form:
-                if to_unit is not None:
-                    if parser==to_form:
-                        output = dict_convert[form_in](output, to_unit)
-                        output = dict_get_value[form_in](output)
-                    else:
-                        output = dict_translate[form_in][parser](output)
-                        output = dict_convert[parser](output, to_unit)
-                        output = dict_get_value[parser](output)
-                else:
-                    output = dict_get_value[form_in](output)
-            elif form_in!=to_form:
-                if to_unit is not None:
-                    if parser==form_in:
-                        output = dict_convert[form_in](output, to_unit)
-                        output = dict_get_value[form_in](output)
-                    elif parser==to_form:
-                        output = dict_translate[form_in][to_form](output)
-                        output = dict_convert[to_form](output, to_unit)
-                        output = dict_get_value[to_form](output)
-                    else:
-                        output = dict_translate[form_in][parser](output)
-                        output = dict_convert[parser](output, to_unit)
-                        output = dict_get_value[parser](output)
-                else:
-                    output = dict_get_value[form_in](output)
 
-    else:
+            if form_in==to_form:
+                output = quantity_or_unit
+            else:
+                output = dict_translate[form_in][to_form](quantity_or_unit)
 
-        raise BadCallError("to_type")
+            if to_unit is not None:
+                output = dict_convert[to_form](output, to_unit)
+            if to_type == 'unit':
+                if is_unit(output):
+                    output=output
+                else:
+                    output = dict_get_unit[to_form](output)
+            elif to_type == 'value':
+                output = dict_get_value[to_form](output)
 
     return output
 
diff --git a/pyunitwizard/parse.py b/pyunitwizard/parse.py
new file mode 100644
index 0000000..1e1102d
--- /dev/null
+++ b/pyunitwizard/parse.py
@@ -0,0 +1,65 @@
+from ._private_tools.exceptions import *
+from ._private_tools.forms import digest_to_form
+from ._private_tools.parsers import digest_parser
+from .forms import dict_string_to_quantity
+from .forms import dict_to_string
+from .forms import dict_translate
+
+def _parse_with_pint(string):
+
+    if string.startswith('[') or string.startswith('('):
+
+        import ast
+
+        end_list = max(string.rfind(')')+1, string.rfind(']')+1)
+        value_string = string[:end_list]
+        unit_string = string[end_list:]
+
+        output=ast.literal_eval(value_string)*dict_string_to_quantity['pint'](unit_string)
+
+    else:
+
+        output=dict_string_to_quantity['pint'](string)
+
+    return output
+
+def parse(string, parser=None, to_form=None):
+
+    if type(string) is not str:
+        raise BadCallError('string')
+
+    parser = digest_parser(parser)
+    to_form = digest_to_form(to_form)
+
+    output = None
+
+    if parser == 'pint':
+
+        if to_form == 'pint':
+
+            output = _parse_with_pint(string)
+
+        elif to_form == 'openmm.unit':
+
+            pint_quantity = _parse_with_pint(string)
+            output = dict_translate['pint']['openmm.unit'](pint_quantity)
+
+        elif to_form == 'string':
+
+            pint_quantity = _parse_with_pint(string)
+            output = dict_to_string['pint'](pint_quantity)
+
+        else:
+
+            raise NotImplementedParsingError(parser, to_form)
+
+    elif parser is 'openmm.unit':
+
+        raise LibraryWithoutStringParserError('openmm.unit')
+
+    else:
+
+        raise NotImplementedParsingError(parser, to_form)
+
+    return output
+
diff --git a/pyunitwizard/tests/openmm_unit/test_convert_with_openmm_unit.py b/pyunitwizard/tests/openmm_unit/test_convert_with_openmm_unit.py
index 81c169f..a223b89 100644
--- a/pyunitwizard/tests/openmm_unit/test_convert_with_openmm_unit.py
+++ b/pyunitwizard/tests/openmm_unit/test_convert_with_openmm_unit.py
@@ -2,59 +2,60 @@
 import pyunitwizard as puw
 import openmm.unit as openmm_unit
 
-def test_from_string_1_a():
+def test_from_string_1():
     puw.configure.reset()
-    puw.configure.load_library(['openmm.unit'])
-    q = puw.convert('1 meter')
-    q_true = 1*openmm_unit.meter
-    assert q == q_true
+    puw.configure.load_library(['openmm.unit', 'pint'])
+    q = puw.convert(1*openmm_unit.meter, to_form='pint')
+    q_form = puw.get_form(q)
+    assert q_form == 'pint'
 
 def test_from_string_2():
     puw.configure.reset()
-    puw.configure.load_library(['openmm.unit'])
-    q = puw.convert('1 meter', to_unit='cm')
+    puw.configure.load_library(['openmm.unit', 'pint'])
+    puw.configure.set_default_parser('pint')
+    q = puw.convert(1*openmm_unit.meter, to_unit='cm')
     q_true = 100.0*openmm_unit.centimeter
     assert q == q_true
 
 def test_from_string_3():
     puw.configure.reset()
     puw.configure.load_library(['openmm.unit'])
-    q = puw.convert('1 meter', to_type='unit')
+    q = puw.convert(1*openmm_unit.meter, to_type='unit')
     q_true = openmm_unit.meter
     assert q == q_true
 
 def test_from_string_4():
     puw.configure.reset()
     puw.configure.load_library(['openmm.unit'])
-    q = puw.convert('1 meter', to_unit='cm', to_type='unit')
+    q = puw.convert(1*openmm_unit.meter, to_unit=openmm_unit.centimeter, to_type='unit')
     q_true = openmm_unit.centimeter
     assert q == q_true
 
 def test_from_string_5():
     puw.configure.reset()
     puw.configure.load_library(['openmm.unit'])
-    q = puw.convert('1 meter', to_unit='cm', to_form='string')
+    q = puw.convert(1*openmm_unit.meter, to_unit=openmm_unit.centimeter, to_form='string')
     q_true = '100.0 cm'
     assert q == q_true
 
 def test_from_string_6():
     puw.configure.reset()
     puw.configure.load_library(['openmm.unit'])
-    q = puw.convert('1 meter', to_unit='cm', to_form='string', to_type='unit')
+    q = puw.convert(1*openmm_unit.meter, to_unit=openmm_unit.centimeter, to_form='string', to_type='unit')
     q_true = 'centimeter'
     assert q == q_true
 
 def test_from_string_7():
     puw.configure.reset()
     puw.configure.load_library(['openmm.unit'])
-    q = puw.convert('1 meter', to_type='value')
+    q = puw.convert(1*openmm_unit.meter, to_type='value')
     q_true = 1
     assert q == q_true
 
 def test_from_string_8():
     puw.configure.reset()
     puw.configure.load_library(['openmm.unit'])
-    q = puw.convert('1 meter', to_unit='cm', to_type='value')
+    q = puw.convert(1*openmm_unit.meter, to_unit=openmm_unit.centimeter, to_type='value')
     q_true = 100.0
     assert q == q_true
 
diff --git a/pyunitwizard/tests/openmm_unit/test_quantity_with_openmm_unit.py b/pyunitwizard/tests/openmm_unit/test_quantity_with_openmm_unit.py
index 7226162..2a36aee 100644
--- a/pyunitwizard/tests/openmm_unit/test_quantity_with_openmm_unit.py
+++ b/pyunitwizard/tests/openmm_unit/test_quantity_with_openmm_unit.py
@@ -5,7 +5,7 @@ def test_1():
     puw.configure.reset()
     puw.configure.load_library(['openmm.unit'])
     openmm_unit = puw.forms.api_openmm_unit.openmm_unit
-    q = puw.quantity(10, 'kJ/mol')
+    q = puw.quantity(10, openmm_unit.kilojoule/openmm_unit.mole)
     q_true = 10*openmm_unit.kilojoule/openmm_unit.mole
     assert puw.similarity(q, q_true)
 
diff --git a/pyunitwizard/tests/openmm_unit/test_unit_with_openmm_unit.py b/pyunitwizard/tests/openmm_unit/test_unit_with_openmm_unit.py
index 31dff0e..f45c2a4 100644
--- a/pyunitwizard/tests/openmm_unit/test_unit_with_openmm_unit.py
+++ b/pyunitwizard/tests/openmm_unit/test_unit_with_openmm_unit.py
@@ -5,7 +5,7 @@ def test_1():
     puw.configure.reset()
     puw.configure.load_library(['openmm.unit'])
     openmm_unit = puw.forms.api_openmm_unit.openmm_unit
-    q = puw.unit('kJ/mol')
+    q = puw.unit(openmm_unit.kilojoule/openmm_unit.mole)
     q_true = openmm_unit.kilojoule/openmm_unit.mole
     assert q == q_true
 
diff --git a/pyunitwizard/tests/test_configure.py b/pyunitwizard/tests/test_configure.py
index 549837e..e666afb 100644
--- a/pyunitwizard/tests/test_configure.py
+++ b/pyunitwizard/tests/test_configure.py
@@ -23,8 +23,9 @@ def test_default_parser():
     assert puw.configure.get_default_parser()=='pint'
 
 def test_init_openmolecularsystems():
-    puw.configure.load_library(['openmm.unit'])
+    puw.configure.load_library(['pint','openmm.unit'])
     puw.configure.set_default_form('openmm.unit')
+    puw.configure.set_default_parser('pint')
     puw.configure.set_standard_units(['nm', 'ps', 'K', 'mole', 'amu', 'e',
                                  'kJ/mol', 'kJ/(mol*nm**2)', 'N', 'degrees'])
 
diff --git a/pyunitwizard/tests/test_similarity.py b/pyunitwizard/tests/test_similarity.py
index 4f208f7..b155846 100644
--- a/pyunitwizard/tests/test_similarity.py
+++ b/pyunitwizard/tests/test_similarity.py
@@ -2,14 +2,15 @@
 import pyunitwizard as puw
 
 def test_1():
-    puw.configure.reset()
-    puw.configure.load_library(['openmm.unit'])
-    output = puw.similarity('1 meter', '1 meter')
-    assert output == True
+    from pyunitwizard._private_tools.exceptions import NotImplementedParsingError
+    with pytest.raises(NotImplementedParsingError):
+        puw.configure.reset()
+        puw.configure.load_library(['openmm.unit'])
+        output = puw.similarity('1 meter', '1 meter')
 
 def test_2():
     puw.configure.reset()
-    puw.configure.load_library(['openmm.unit'])
+    puw.configure.load_library(['pint', 'openmm.unit'])
     output = puw.similarity('1 meter', '1 kilometer')
     assert output == False
 
@@ -21,7 +22,7 @@ def test_3():
 
 def test_4():
     puw.configure.reset()
-    puw.configure.load_library(['openmm.unit'])
+    puw.configure.load_library(['pint', 'openmm.unit'])
     output = puw.similarity('1 meter', '100 cm')
     assert output == True
 
@@ -49,5 +50,19 @@ def test_6():
     output = puw.similarity(aa, bb)
     assert output == False
 
+def test_7():
+    puw.configure.reset()
+    puw.configure.load_library(['pint','openmm.unit'])
+    aa = puw.quantity(4,'mm')
+    bb = puw.quantity(0.4,'cm')
+    output = puw.similarity(aa, bb)
+    assert output == True
+
+
+
+
+
+
+