18 C.F.R. § 154.310
Zones
If the company maintains records of costs by zone, and proposes a zone rate methodology based on these costs, the statements and schedules in § 154.312 and § 154.313 must reflect costs detailed by zone.
If the company maintains records of costs by zone, and proposes a zone rate methodology based on these costs, the statements and schedules in § 154.312 and § 154.313 must reflect costs detailed by zone.