I need a help, I need to calculate an interval of time in 1 hour and divide your result by 12.

I have a table in my database that receives data from date and time and a value field in a cycle of 5 minute in 5 minute cycle I have 12 values ​​in 1 hour. I need to sum ​​the values ​​of this period of 1 hour and divide its value by 12.

How could I do this using a formula of the crystal 2011? was trying to use the DateDiff passing a parameter interval of time to filter, but I had no success.

My parameter using the type Date and Time, Static, Allow range values​​.

DateDiff ("h", {TB_Dados.Timestamp}, {?MyParameterDateRange})

thank you.