Derive Period Balances from YTD Balances

I was wondering if someone might have a suggestion on what would be the best approach to derive period balances from YTD balances (assuming that each year has 12 periods)

Sample scenario --> the expected result is shown in the last column

Cost_Center Project_Num Period YTD_Amount Period_Amount (to be calculated)

0100                  111                 200812
500                          500
0100                  111                 200908
100                          100
0100                  111                 200909
120                           20
0100                  112                 200811
35                            35
0100                  112                 200902
-10                          -10
0100                  112                 200903
0                            10
0200                  111                 200811
45                          45
0200                  111                 200901
30                          30

Any suggestion would be appreciated

Thanks,

Milos Received on Fri Sep 18 2009 - 11:25:58 CDT