10 U.S.C. § 623 — Establishment of promotion zones

(a) Before convening a selection board to consider promotion above first lieutenant or lieutenant (junior grade^*), the military department Secretary must establish a promotion zone^* for each grade and competitive category the board will consider.

(b) The Secretary must choose how many eligible officers in each grade and category go into the zone. The choice must be based on estimates of: (1) how many officers will be needed in the next higher grade in each of the next five years; (2) how many officers will be serving in that higher grade in each of those years; (3) if section 523 applies to the grade, how many officers that section authorizes to be on active duty^* on the last day of each of the next five fiscal years; and (4) how many officers should be put in the zone in each year so officers in those years have relatively similar chances for promotion.