Options for setting "nominal" weight in analysis tab

[SigmaRelief]

On the analysis tab, assuming 0% based only on the 2mm/s rate for a particular temperature underestimates the underextrusion at low temps. In a multi temp series, setting the baseline to the highest observed weight (probably the slow hot blob) may give better absolute numbers. This is trivial to add in Excel, but many users probably don't check the underlying formulas.

An option to fill in measured weight from a 200mm length of filament could also be an interesting addition even if there are better calibration tests for dialing in the last few percent of flow multiplier for real world performance.