The board shall, from the returns or reports of the tests, prepare a register or eligible list, for each grade or class of positions in the classified service, of the persons who attain such minimum mark as may be fixed by the board for any part of such test as fixed by the rules of such board and who are otherwise eligible. Such persons shall take rank as candidates upon such register or list in the order of their relative excellence as determined by test, without reference to priority of time of test. The board shall provide by its rules for promotions in such classified service on a basis of ascertained merit in service, seniority in service and special test. The board shall submit to the appointing power for each promotion the names of not more than three applicants having the highest rating. The method of testing and the rules governing the same and the method of certifying shall, as far as possible, be the same as provided for applicants for original appointment.