All RealData products will prompt you to save your file in the best format. You can however change the file format if you wish.
When saving the workbook, you should use file format “.xls”, which is the Excel 2003 (and earlier versions) compatibility file format or the “.xlsm” Excel 2007 (or later) format. Do not use file format “.xlsx”, because that will strip out all macro code, and the software will not work correctly.
The .xlsm format does have the advantage of a significantly smaller file size.