Calculated Fields of difference of hours

Hi, I need to create a formula in a calculated field. The formula has to calculate the difference between two dates (creation date and now) and give me the result in hours, because in the report I have to show the time in hours from the creation date until now.

Until now I tryed those formulas:


{datediff({P!}; {P0}; hours)}




where P1 is now and P0 is the creation date.