Section 151(5)(c) in The Naval Ceremonial, Conditions Of Service And Miscellaneous Regulations, 1964
(c)For purposes of this sub-regulation reckonable commissioned service means the actual commissioned service rendered, except that an ex-Branch List Officer shall be permitted to reckon, on the date of substantive promotion to the rank of Lieutenant-Commander, 11 years commissioned service or the actual commissioned service, including service in the Branch List, whichever is less.