Instead of defining it numberic and entering the format .. create a variable that has the format and then define it as character and use the following expression:

TRANSFORM(MyNumber, cFormat)


>I have a lot of calculated fields in report.
>
>Before viewing report, I want to allow user to select three different
>precisions for all numeric field for reports. One, two or zero digits after points :
>
>999 999 999.99
>999 999 999.9
>999 999 999
>
>Format field in reprot designer accepts only constant format
>expressions.
>How to use three different format expressions in same format for numeric fields ?