( 1 ) THESE appeals under letters patent are directed against the judgment and order of a learned single judge, dated 31-5-2005 in WP Nos. 6372-73; 6376 and 6382 of 2003. ( 2 ) THE respondents had claimed for directions to the appellant (Bureau of Indian Standards, hereafter BIS) to promote them as Scientists-D in the pay- scale of Rs. 12,000-375-16,500/- on the date of their completion of 5 years of service in the lower grade, under a scheme known as the Flexible Complementing Scheme (hereinafter referred to as `the Scheme ). ( 3 ) THE BIS is governed by statutory regulations. The relevant provision, viz Regulation 9 of Bureau of Indian Standards (Recruitment to Scientific Cadre) Regulation, 1988, read as follows:"9. Promotion to the Posts up to System Scientist-E [director (selection Grade)]" (1) The selection for promotions shall be made from amongst the scientific cadre officers serving in the next lower grade by the standing staff committee of Selection Committee `a as the case may be, on the recommendations of the Assessment Committee appointed by the Director General under sub-regulation (3 ). Selection of officers for promotion shall be made on the basis of assessment procedure as laid down by the Executive Committee which shall take into account qualifications performance, merit, seniority, potential, annual confidential reports for previous five years and interview. (2) The promotion of Selected officers to next higher grade up to the System Scientist-E shall be made in the same manner as laid down in the Scheme of Flexible Complementing formulated from time to time by the Department of Science and Technology for promotion of Scientists in scientific organizations under the Central Government and shall be effective from the date of eligibility. ( 4 ) THE BIS adopted recommendations of the Fifth Central Pay Commission, with effect from 1-1-1996, and implemented the scheme. The scheme contemplated promotion, after completion of certain prescribed periods of service, in relation to each post (known as the residency period ). These pertained not only to posts, but also to scales of pay. The relevant residency periods, were as follows: