The mayor, with the consent of the commission, shall appoint a clerk who shall also act as secretary for the commission and who shall keep the records for the commission, prepare all reports made to it and keep a record of all examinations held under its discretion and perform such other duties as the commission may prescribe. From the returns or reports of examinations made by the commission, the clerk shall prepare a register for each grade or class of position in the classified service of the city, of the persons whose general average standing upon examinations for such grade or class is not less than the minimum fixed by the rules hereinafter provided therefor, and who are otherwise eligible; and such person shall take rank upon the register of candidates in order of their relative excellence, as determined by examination without reference to priority of time of examination.