37 U.S.C. § 205: Computation: service creditable

all periods of active service as an officer, Army field clerk, flight officer, aviation midshipman, or enlisted member of a uniformed service; a regular component of a uniformed service; a reserve component of a uniformed service; the Space Force; the Regular Army Reserve; the National Guard; the National Guard Reserve; the Naval Militia; the National Naval Volunteers; the Navy Reserve Force; the Army without specification of component; the Air Force without specification of component; the Marine Corps Reserve Force; the Philippine Scouts; or the Philippine Constabulary; for a commissioned officer in service on June 30, 1922 , all service that was then counted in computing longevity pay and all service as a contract surgeon serving full time; all periods during which he held an appointment as a nurse, reserve nurse, or commissioned officer in the Army Nurse Corps as it existed at any time before April 16, 1947 , the Navy Nurse Corps as it existed at any time before April 16, 1947 , or the Public Health Service, or a reserve component of any of them; all periods during which he was a deck officer or junior engineer in the National Oceanic and Atmospheric Administration; all periods that, under law in effect on January 10, 1962 , were authorized to be credited in computing basic pay; and on a temporary disability retired list, honorary retired list, or a retired list of a uniformed service; entitled to retired pay, retirement pay, or retainer pay, from a uniformed service or the Department of Veterans Affairs, as a member of the Fleet Reserve or the Fleet Marine Corps Reserve; or a member of the Honorary Reserve of the Officers’ Reserve Corps or the Organized Reserve Corps. A period of time may not be counted more than once under subsection (a). The periods of service authorized to be counted under subsection (a) shall, under regulations prescribed by the Secretary concerned, include service performed by a member of a uniformed service before he became 18 years of age. Notwithstanding subsection (a), a commissioned officer may not count in computing basic pay a period of service after October 13, 1964 , that the officer performed concurrently as a member of the Senior Reserve Officers’ Training Corps, except for service that the officer performed on or after August 1, 1979 , other than for training as an enlisted member of the Selected Reserve may be so counted. Notwithstanding subsection (a), a period of service described in paragraph (2) of a member who enlists in a reserve component may not be counted under this section. Service performed while a member of a reserve component under an enlistment under section 12103(b) or 12103(d) of title 10 before the member begins service on active duty under such section (including a period of active duty for training) unless the member performs inactive-duty training before beginning service on active duty or active duty for training; Service performed while a member of a reserve component under an enlistment under section 513 of title 10 (other than a period of active duty to which the member is ordered under chapter 1209 of title 10 or another provision of law). Notwithstanding subsection (a), the periods of service of a commissioned officer appointed under section 12203 of title 10 after receiving financial assistance under section 16401 of such title that are counted under this section may not include a period of service after January 1, 2000 , that the officer performed concurrently as an enlisted member of the Marine Corps Platoon Leaders Class program and the Marine Corps Reserve, except that service after that date that the officer performed before commissioning (concurrently with the period of service as a member of the Marine Corps Platoon Leaders Class program) as an enlisted member on active duty or as a member of the Selected Reserve may be so counted. The rate of basic pay for an enlisted member in the grade E–9 while serving as Senior Enlisted Advisor to the Chairman of the Joint Chiefs of Staff or as Senior Enlisted Advisor to the Chief of the National Guard Bureau shall be the same as the rate of basic pay for an enlisted member in that grade while serving as Sergeant Major of the Army, Master Chief Petty Officer of the Navy, Chief Master Sergeant of the Air Force, Sergeant Major of the Marine Corps, or Master Chief Petty Officer of the Coast Guard, regardless of cumulative years of service computed under section 205 of title 37 , United States Code. Paragraph (1) shall apply beginning on the date on which an enlisted member of the Armed Forces is first appointed to serve as Senior Enlisted Advisor to the Chairman of the Joint Chiefs of Staff.”