The Oscilloscope quality measure should calculate quality for the A-B and A+B traces

[sfentress]

When a student answers a question in an AC activity, the activity author can write a script to check if the student set up the breadboard correctly. One of the pieces of meta information that is useful to an author is to see whether or not the OScope has been scaled correctly. This allows the activity to provide feedback to the student, telling them to scale the oscope if they get the wrong answer.

Currently we calculate the oscope scale quality for the two traces (pink and yellow). We would also like to add the scale quality for the A-B and A+B combo traces. These traces are visible when the pink and yellow traces are both on the screen, and one of the combo buttons on the oscope is pressed.

When a question is being scored, it calls getGoodnessOfScale() on oscilloscope.js, which returns an array of two scale qualities. When the feature is completed, it should return an array of size 4, with the A-B trace being index 2 and A+B being index 3. If the respective button is not pressed, the value should be null.

Note that since only one of the combo buttons can be active at any time, there will always be at least one null value in the array.

This can be seen here:

http://sparks.portal.concord.org/sparks-content/activities.html#oscilloscope-scale-quality

You can see the current result by clicking the "Submit" button. When the feature is complete, we should get a value for either A-B or A+B if the student clicked one of those combos, and "null" if they didn't (instead of "undefined").

[jnowosinski]

I am working on that issue.