Provisional Rules of Procedure
Chapter IV: Presidency
Rule 18
The presidency of the Security Council shall be held in turn by the members of the Security Council in the English alphabetical order of their names. Each President shall hold office for one calendar month.
Rule 19
The President shall preside over the meetings of the Security Council and, under the authority of the Security Council, shall represent it in its capacity as an organ of the United Nations.
Rule 20
Whenever the President of the Security Council deems that for the proper fulfillment of the responsibilities of the presidency he should not preside over the Council during the consideration of a particular question with which the member he represents is directly connected, he shall indicate his decision to the Council. The presidential chair shall then devolve, for the purpose of the consideration of that question, on the representative of the member next in English alphabetical order, it being understood that the provisions of this rule shall apply to the representatives on the Security Council called upon successively to preside. This rule shall not affect the representative capacity of the President as stated in rule 19, or his duties under rule 7.