N.J. Stat. Ann. § 43:13-23

As used in this article, "a year of service" shall consist of such part of the calendar year as the life guard force is normally employed and the "year's salary" means the salary a life guard receives during the time of his normal employment in any calendar year. If the salary is payable on a per diem basis the pension commission may determine the length of service and the amount of the year's salary by averaging the salary theretofore received by the life guard or officer during the then past three years or in any other equitable manner and may determine in that case what constitutes a year's salary and a year's service.