BJG2005 wrote:
I've been working with a large, old spreadsheet that I inherited. It has
~150 worksheets.

Occassionally, a row of formula won't update. That is, I change some values
on 1 worksheet, but when I get to another, the new values are not reflected
in a formula that might be merely adding 2 cells from the first sheet. I
have and keep auto calc = "on". I can go to the cell and hit "F9". The
value doesn't change.

If I re-type the exact formula, it correctly calculates and shows the
correct value. If I drag and auto fill this formual across the row,
essentially replacing each formula with an exact duplicate of what it already
had, the value re-calculate and display the correct value.

What could cause this? More importantly, how do I fix it?

Thank you, in advance for any suggestions.

Try inceasing your Iterations Tools menu/ Options / Calculaton /
Iterations. At least 100. if already 100, increase to 500.

ed