Period Counter

Key Period Counter of function Period Value in IRSrefers to an optional index of an accrual period relative to which information is requested.
The very first accrual period is assigned the number 1.
Given any date, the index of the accrual period containing that date may be calculated using the function Period Counter
Look at that function's description for more details.
If set to any non-positive number or omitted alltogether, the index of the period is not explicitly defined, but it may be still implied by the date entry in key Date in Period