Éiríonn an sruth borrtha ina shruth seasta tar éis bíog ghairid. Is gá I2t carnach an tsrutha borrtha a chur i gcomparáid le I2t coibhneasta an fhiús, is é sin, an I2t coibhneasta I2t den chuisle/I2t den fhiús séidte. Is é I2t carntha an luach fuinnimh a carntar le himeacht ama.
