A relative reference in @if statements.

True—if the period is the first period in the model

False—if not

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.