(a) Conduct all examinations for admission to or promotion in the
  classified service of the internal-revenue district in which the board
  is located.

  (b) Conduct such other examinations as the Commission may direct.

  (c) Mark the papers of such examinations as the Commission may
  direct.

2.  The papers of every examination shall be marked under the direction of the Commission, and each competitor shall be graded on a scale of 100, according to general average determined by the marks of the examiners.

  3.  Immediately after the general average shall have been ascertained
  each competitor shall be notified that he has passed or has failed to
  pass.

4.  No competitor who has failed to pass an examination and no eligible during the period of his eligibility shall be allowed reexamination unless he shall furnish satisfactory evidence to the Commission that at the time of his examination he was, because of illness or other good cause, incapable of doing himself justice; and his rating on such reexamination, if an eligible, shall cancel and be a substitute for his rating on his previous examination.

5.  All competitors whose claim to preference under section 1754, Revised Statutes, has been allowed by the Commission who attain a general average of 65 per cent or over, and all other competitors who attain a general average of 70 per cent or over, shall be eligible for appointment to the place for which they were examined, and the names of all the eligibles shall be entered in the order of grade on the proper register of eligibles.

  6.  When two or more eligibles are of the same grade, preference in
  certification shall be determined by the order in which their
  application papers were filed.

  7.  The period of eligibility shall be one year from the date on which
  the name of the eligible is entered on the register.

  INTERNAL-REVENUE RULE IV.

  1.  All vacancies, unless filled by promotion, reduction, transfer, or
  reappointment, shall be filled in the following manner: 

(a) When a vacancy occurs in any district, the collector thereof shall report the fact to the Commissioner of Internal Revenue, stating the class in which the vacancy occurs and whether in his judgment the place should be filled.  If the Commissioner decides that the good of the public service requires that it be filled, he shall request the secretary of the board of examiners of that district to certify to him the names of persons eligible to the vacant place.

(b) If fitness for the vacant place is tested by competitive examination, the names of the three eligibles highest in grade on the proper register who have not been three times certified shall be certified; but if the request indicates the sex