Why does a file asked to be saved without making change? (and I have no external links)

[w109dmd]

I have 3 similar files. For some reason, one of the 3 files needs to be saved even if I don't make any changes. I know it is a mistake, but each file has 30 worksheets and it is hard to find the mistake. I have checked to see if I have external links, but I have no external links. What else would require me to save a file without making any changes myself? My other two files (that do not need to be saved unless I change something) have the same internal links (functions/formulas). So I need to find my mistake.

Thanks!

[TMS]

Probably NOT a mistake

If any cell has a volatile function in it, it will cause the workbook to be calculated, and hence change.

Typically, this could be because you are using =TODAY() or =NOW() in a formula, or formulae.

Regards, TMS