Two ways to do this. Either modify the formula in B2 to:

=IF(OR(A1="",A2=""),"",A1-A2)

Or use Conditional Formatting with the condition:

=OR(A1="",A2="") and just a simple A1-A2 formula

Just be careful with the quotes, as Excel sometimes doubles them up for me.
So, if you get something like ="OR(A1="""",A2="""")", you need to edit the
formula

I would suggest the formula is the simpler approach

Regards

Trevor


"John" wrote in message
...
I have 2 cells which I select entries from a drop-down (A1 and A2) B2 then
does a simple subtraction of whats selected in A1 and A2

A user can select only A1 or A2, this would be incomplete thus I want in
this instance to "blank" out the value returned in B2 i.e. with white
font, as the result is not very meaning full

How would I do this under conditional formatting in B2

I thought of something like this if(or(A1=" ",A2=" "), but don't think you
can use "IF" in conditional formatting


Thanks