variable in planning area

Hi,

How to give a variable for eg: target currency in the multiple planning area. This variable should be filled by fixed value USD. Based on this calculations are done and the output should be amount in usd.

As variables types are characteristic values, hiererchy, numetic values and attributes. how to get this. I don't have any characteristic to be assigned to the variable in the infocube. The variable should be like static with fixed value USD.

How to achieve this?