QReport : Personnal functions in QrExp

Thanks to read !

    We having problem with QrExp componment. In the Expression proprety of
the QrExp comp. We try to use one of our own function:

Ex :


We use the unit in the uses clause.

Is that possible to use one of our own function or are we limited by the
Sum, Count, Avg... componment function ????

Help we be a lot apreciate