A relative reference in @if statements.
You can divide a year into quarters, enabling aggregate half year periods, or divide a year into halves, which would not make these aggregate periods. Time period detail is determined in Defining, Deleting, and Displaying Time Periods.
True—if the period is a half-year period whether or not it is an aggregate period
False—if not
If a model has 2006 in years and 2007 in half years, this formula:
@if(@ishalf, 1, 2)