For those who may have used or want to use my G/T spreadsheet tool I have discovered a defect in one cell's formula.
The defect is due to regression of a much earlier fix, so your existing models may or may not be affected. The error would usually be very small and you might not notice it unless you increased displayed precision. Nevertheless, it is a defect and should be fixed.
An updated version of the spreadsheet GT.xlsm is at https://github.com/owenduffy/xl/src .
If Microsoft has frightened you off using spreadsheets with macros, you could use this with macros disabled, it just stops the green sort button working, all the cells still calculate properly.