Where service for which a member receives credit, either prior to or during membership, is on a tenure which is temporary, seasonal, intermittent, or part time only, the member shall receive credit as continuous service for that proportion of the time he or she held the position as the time he or she actually was engaged in the performance of the duties of the position bears to the time required to perform the same duties in a full-time position.

A “year of service” in the position shall be construed to mean the time during which the member has earned one full year of credit, calculated as provided in this section.