# Calculation Engine - Formula Function Reference
## Frequently asked questions
The up-to-date F.A.Q. page for PHPExcel can be found on [http://www.codeplex.com/PHPExcel/Wiki/View.aspx?title=FAQ&referringTitle=Requirements][1].
### Formulas don’t seem to be calculated in Excel2003 using compatibility pack?
This is normal behaviour of the compatibility pack, Xlsx displays this correctly. Use PHPExcel_Writer_Excel5 if you really need calculated values, or force recalculation in Excel2003.
[1]: http://www.codeplex.com/PHPExcel/Wiki/View.aspx?title=FAQ&referringTitle=Requirements
