Calculations for relative time

[Cognosnewbie26]

Hi,
My time dimension looks like below:
Year
Quarter
Month
Date
I want to create a calculation for Prior Time ( it can be prior year, quarter, month or same date of previous year)
I was wondering if I can create a calculation in such a way that it is able to gauge  if it is a year, quarter, month or date is pulled for the current year
For e.g
                           Month     PYMonth
Account No

In the above case if I pull the 'Month' then it should be able to calculate the amount for the PYMonth