auto updating cell values help
 

Hello all,

I am having a bit of a problem trying to figure out how to write this code.
Basically, I have in Cell A1 a value (ie 100) and cell A2 is a drop down
validation box with 2 possible responses (YES & NO). What I need is a code,
that will automatically update the value of A1 if cell A2 is set to YES.
It's a count of what is left.

ie. A1 = 100 and you select YES for A2, then A1 needs to update to 99
(A1.value - 1), but if A2 is NO, then no change is made to A1.

Any help provided will be greatly appreciated!!

Thomas