Ahh - ok, thats interesting.
In that case we should surly integrate!
I started a parallel system with two classes:https://sourceforge.net/p/free-cad/code ... ase/Unit.hhttps://sourceforge.net/p/free-cad/code ... Quantity.h
Quantity is planed to have its own parser (Quantity.y and Quantity.l).
I aim for a complete units capability which allow calculation and comparison of non trivial dimensions like e.g. :http://www.dimensionengine.com/
But fore sure it makes sense to integrate it! A spreadsheet in FreeCAD without units capabilities is anyway of limited use...
My plan was/is to have the parser and then create a Qt input class to replace all QDoubleSpinBoxes and other fields to input Values/Quantities.
Replace all properties in Features (which hold doubles) to hold and check Units and do the translation from user to intern and the other way around...
In the long run I want to have every expression or double value in FreeCAD has a Unit attached (Quantity). Basically means no bare doubles in FreeCAD anymore
So would be great you could incorporate this facet in your expression parser! The I could concentrate on the input element. You can use that also in your spreadsheet gui....