Whenever any elected assessor, or, in townships of the first class, any assessor, assistant township assessor or assistant triennial assessor, whose duties pertain to making assessments for purposes of county taxation, shall be required to travel to the county seat of his county, or to any place of sitting of the county commissioners elsewhere than at the county seat, he shall receive from the county mileage at the rate of three cents a mile for each mile necessarily traveled, both going and returning, in addition to the per diem compensation for services allowed by this act.
72 P.S. § 5020-308