definition of a rolling month.
P:\Con-perm\Croling\rolling month. 12-Month Rolling Period. Definition (567 IAC 22.100): A period of 12 consecutive months determined on a rolling basis with a new 12-month. period beginning on the first day of each calendar month. Example calculation. Assume a permit limits an emissions unit to 6,000 hours of operation per 12-month rolling period and the unit is.