Sorry guys but I've tried searching and this question must be so dumb it
isn't even worthy of a prior post.

Anyway, I'm fiddling with data (question to be asked later) and somehow my
displayed column headings are now numbers. Before they were letters. So
when I click on a cell (e.g. first cell is now listed as R1C1) but I want it
listed as A1. What did I do to make it this way. Even opening up a new
spreadsheet displays the same column number.

I'm asking because I know future formulas will be more difficult and most
folks have it listed as column letters.

Thanks