If you've got 99 cells with identical formulas, and one without, it's not far fetched for Excel to speculate that there may be a mistake (particularly if they'r

If you've got 99 cells with identical formulas, and one without, it's not far fetched for Excel to speculate that there may be a mistake (particularly if they're within X% of being identical). At which point it can provide a simple, non-intrusive hint. It already does this, actually. Enter some data in two columns, like: 4 1 2 3 5 6 3 2 4 2 2 1 Then enter a sum formula in the next column like =SUM(A1:B1) and drag it all the way down. Change one in the middle to something else, like =SUM(B3:B3) instead of =SUM(A3:B3) and a little green arrow appears in the corner. Hover above it an it explains there is an "inconsistent formula".