Calculations for Time Drill-down Menu

[#1]

Hi Experts,

I have created drill down menu for Time(Year-Month-Day-Minute).I have values available for days of month.

ex. for month-5

day    value

1        a

2        b

3        c

..        ..

31      d

For Month value, I want calculate average of day values.

for month 5, monthVal= avg(a+b+c+...d)

So when i drill up from day to month, it will show me average value of all days(monthVal) of that particular month.

Please help

Thank You