Section 2(1)(iii) in All India Services (Death-Cum-Retirement Benefits) Rules, 1958
(iii)In the case of a member of Service who, while on leave preparatory to retirement is confirmed in the higher post which he held in an officiating or temporary capacity before proceeding on such leave, his substantive emoluments in the higher post, which he would have drawn had he been on duty, shall be taken into account for the purpose of calculation of his average emoluments.