How to Off set the variable range ?

experts !

i have created a variable on ofiscper, and it gives a range for that. ( e.g. 001/2009 - 012/2009 ) . everything works good. but i have to show values for the same range for previous year too.. so i thought that off set should be working. But i am not gettting the correct results if i use off set to ( -1 ).

can we use offset for a variable whcih takes range ?

what are my options ?

Thaks