my pet peeve - yup - that little exasperating option that users check on to infinitely p!$$ off others... you could be changing formulae furiously and not getting proper results without it dawning until much later to check that darn Calculation Mode (ALT > M > X).
well, looks like Excel does, sort of, warn you with a message in the Status Bar at the bottom-left of the screen, where it shows the word Calculate - if Manual Calculation option has been set and there are cells that have been marked as 'to-be-calculated' by Excel. it still takes me a couple of seconds before i look there, but much better than changing formulae whole-scale without reason.
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