Hi Jason, thanks for jumping in.

You're right, if the input is 12345 it will return 12-345 and not 12-34-5.

I didn't mentioned it, but for years the requirement was 12-34-5, only now
they came up with 12-345.

The spec for now (conditional, I know) is not more than 5 digits and 2 or 3
letters.
Possible combination, where y = letter, x = digit:
yyy-xx-xx
yy-xx-xxx
xxx-yyy
yy-xx
xxx-yy-xx
xxx-yyy-x

So for now the CF is covering that.

I hope the power in charge will not change his mind and ask for AND 12-34-5
AND 12-345.

I don't see how to tackle that without a sort of additional 'choice'.
However, the combination letters/digits is 'state dependable'.

The problem is that we do not always have the state information at the
moment the user has to fill in the letter/number combination. 

I think that with a script trigger on the state field I can check for the
correctness of the returned value and, if need be, call the CF again.

My previous calculation, that I changed in a CF years ago when CFs became a
feature, was good for over 12 years. 
My hope is that this change will stand that long also.

However Jason, I'm always willing to learn how to tackle more digits....

In Kindness

JW