Thanks for that..
of course you're right!.... I worked out the calculations without having them stored in a variable (as you said) and used your previous syntax example as a guide to using them

One thing I would like to to be able to do is prefill the original TIB (A1 and A2) with values; either from a dropdown list or just with some relevant value , as I get various displays in the fields with expressions till these are filled in properly.
This is getting to be fun.. never though it would happen!
Thanks guys