For what it's worth, my spreadsheet module implements expressions (including units!) with dependency tracking of properties already. The only thing left is to make it adhere to the undo framework in FreeCAD. Please see https://github.com/eivindkv/free-cad-co ... adsheetMod for the details. Now if I could just get my house remodelling work done, so I could get more spare time to spend on FreeCAD...
I pulled your branch here
https://github.com/eivindkv/free-cad-co ... adsheetMod
but I could not get it to build on Kubuntu 12.04.4 with either OCC 6.5.0 or OCE master 0.16. The above zip file contains a txt file which I copied and pasted the command line error messages for the first attempt with OCE master 0.16 and then I tried with the default Ubuntu 12.04 OCC 6.5.0 it also failed but I have included all the command line out put the second time.
I hope this helps.