You must be opening a workbook that has been set to manual, that will
change it. Check the settings on the files you have opened.

TJAC wrote:

My computer switches in the Tools -- Options menu and then the calculation
tab from automatic to manual by itself. I will select automatic one day and
the next day I will be working in Excel and suddenly it has switched to
manual again. What can I do so that it remains on Automatic since I am not
changing it? It's really annoying because sometimes I don't think about it
since I didn't switch it to begin with.

Thanks for your help!