Stop Excel from updating formula after a criteria is matched

Question

Is there a way to stop a formula from updating after a certain criteria is matched?

For example:

A1 = 1
B1 = \'=A1*2\'

Lets say thi

Answer 1

You can use a circular reference. For example, in A2 I entered

=IF(NOW() < C1,2*A1,A2)

C1 has the value 6/24/2015 14:39

I enable circular references underneath file > options > formulas. Prior to 2:39 my time I was able to change the value of A1 and see A2 change. That was 2 minutes ago (in my time zone). Now when I change A1 the value of A2 stays fixed.