I know I have done this before, but I am at a different company now and can't look up how I did it. I have created a Project Tracker list with several columns, including Status, % Complete, and Completion Date.
I want to allow the "Completed" choice for Status only if the
% Complete = 100and the
Completion Date is not blank. I am not sure exactly what to put in the formula field for Column Validation. I think it's something like this:
[Status] = Completed if [% Complete] = 100% AND [Completion Date] = not blank