Section 3(3)(a) in The Indian Administrative Service (Regulation of Seniority) Rules, 1987
(a)[ for the service rendered by him up to twelve years, he shall be given a weightage of one year for every completed four years of service, subject to a minimum of three years; [Substituted by Notification No. G.S.R. 495 (E), dated 5.5.2016 (w.e.f. 6.11.1987).]