Is first period
A relative reference in @if statements.
If the first quarter of 1998 is the first period in the model, this formula:
@if(@isfirstpd, 1, 2)
returns 1 for 1Q98, and 2 for other periods.
If you delete 1998, the formula in the previous example returns 1 in the first period of 1999, and 2 in subsequent periods.