Using a Lag key figure in the calculation of another key figure

[jez_lawson]

Hi Experts,

I am trying to create a KF where the future periods show a forecasted value and the historical periods show a forecast that is stored in lag key figure.  I have not been able to determine if it is possible (and if so how) to refer to a specific Lag in the calculation.  

Specifically I want to pull Lag 2 for the past periods.  I know how to handle the future/past split (as I have several key figures working this way) but I am struggling to pull the lag value (or any to put any attribute specific condition) into the calculation spec,

Thanks,

Jez