thank you DBlank for your answer,
actually i made a formula which calculate a duration of time based on some functions, and i want to use the duration returned by this formula inside another formula.
so how can i call that formula or rather the value returned form inside the new formula that i want to create ??
one more question please, what about total or summary fields (i don't know the exact name in english because i'm using a french version of crystal report ) whcih calculate sum,avg,max,min... ? can we do the same thing with them ? i mean catch the value returned by them ??
thank you a lot for your help