Help required for new Series

Hi All,

I'm facing issue while creating one of new required series:

Requirement:

Planners want to measure bias between Sales Forecast and Mkt. Forecast in current month and store the value for trend analysis. (Let me give eg)

Feb Trend % = Sales Forecast / Mkt. Fcst

Jan Trend % = Sales 1M Lag /Mkt. 1 M Lag

Dec Trend % = Sales 2M lag/Mkt. 2M lag

                          .

                          .

                          .

                          .

                          .

                          .

                and so on till Lag 12.

All these trend has to be stored in single series for accuracy measurement.

How the data moves to Lag: As part of monthly custom archival process we move the existing forecast to Lag 1 similarly previous month forecast to lag 2 and so on till lag 12.