S&OP offset Function

Hello S&OP Community

At my customer, we have multiple requirements to show in
the data view in the current month the current month’s Forecast as well as the
Forecast from the same month the previous year.

Time                                           11/2013                12/2013                   1/2014                      2/2014

Forecast                                       100                         120                         200                         170

Forecast previous year                 90                          130                         190                         180

I know that there is an offset function in S&OP which
we can use to address this issue. Can someone please provide further
information on how to use the offset function and maybe even some
documentation?

Thank you,

Jens