>>I think the problem is that the expression isn't evaluating. I've tried putting it in the InteractiveChange Event as well.
>
>Perhaps the "Conc"$this.value isn't true?
>
>Maybe you could use: "CONC"$Upper(This.Value)
>
>The 80/20 rule applies to coding the user interface:
> 80% of your code is to trap 20% (or less) of the possible inputs.
>
>Also: Users will inevitably find the one case you didn't code for.

I prefer ATC('conc',This.Value) > 0 to "CONC" $ Upper(This.Value)