8(4)A person who was not a contributor during the school year ending June 30, 1978, and who subsequently becomes a contributor, shall be required to elect to purchase active military service within one year of becoming a contributor, and if an election is made, an amount shall be paid based on the salary in effect at the time of becoming a contributor and the contribution rate in effect at the time of making the election, together with interest calculated in accordance with subsection 4(2) of this Regulation from date of becoming a contributor to the date of election.