What is the best way to rollup the first 3 months of a 24 months period?

[cadetron]

I have a project that was handed to me.  I have to display the trend on 4 different measures over a 24 months period with the most recent three to be at the Trip_Leg detail level.

The data is as follow you have a Trip record and within a trip you will have a Leg_A or Leg_B or Both.

       Trip

         /\

        /  \

Leg_A  Leg_B

[MK9885]

Can you explain more with your scenarios?

As in if you select particular Year or Month what Yr or Month data should it show..?

[cadetron]

The most recent 3 including selected needs to be rolled up.