XIV. Whenever the head of an office shall notify the board of examiners for such office that a vacancy which he desires to fill exists in any grade above the lowest not excepted from the rules and regulations for the civil service, the board will fix a time for holding an examination for the purpose, and at least five days before the same is to take place will cause a notice to be posted in a conspicuous place in the office, stating the grade and group of the vacancy, the date of the examination, and that the vacancy is to be filled by a competitive examination of applicants from the next lower grade, unless none in such lower grade be found qualified, when those in the next lower grade may compete, or, if there be none in any of the lower grades qualified, competition will be open to applicants. In any examination for promotion, if the competitors from the next lower grade shall not exceed three in number, the board may, at its discretion, open the competition to the next lower grade or below, as they may deem best; and furthermore, if such promotion would probably occasion vacancies requiring other promotions, the board may combine in one the necessary examinations for such promotions. No person who has been examined in any grade for promotion and failed to receive such promotion shall again be admitted to examination within six months, but in the meantime his general average, as ascertained by such examination, may be brought into competition, as provided in Regulation XI. XV. The examination will be held upon the general subjects fixed for examinations for admission to the lowest grade of the group and upon such other subjects as the general nature of the business of the office and the special nature of the position to be filled may seem to the board of examiners to require. Due weight will be given to the efficiency with which the several candidates shall have previously performed their duties in the office; but no one who shall fail to pass a minimum standard of 75 per cent in the written examination will be certified for appointment. XVI. If no applicants from within the group shall be found competent, an examination will be held of all who shall make application in accordance with the regulations governing applications for admission to the office, after due public notice by the head of the office. The examination will be conducted in accordance with the provisions for admission to the office, as required by the fourth rule[31] for the civil service promulgated December 19, 1871, but the nature of the examination will be the same as in any previous examination for the same vacancy. XVII. The list of names from which the appointment is to be made will be prepared and certified in the manner provided for admission to the lowest grade.