Where to create time shift variable to input in RSCUR

Hi,

I am trying to create a new currency translation type in RSCUR. In the time ref tab i opted variable time reference and selected "Beginning of the week" and chosen info object 0CALWEEK. I wanted to create a new variable and use in time shift for variable. Can any one suggest me where i have to create the variable for it to be available as a selection for time shift variable field.

Looking forward for the response.

Thanks.

Sravya