ministry as may be agreed, in accordance with the practice prevailing in the receiving State which shall be applied in a uniform manner. 2. The order of presentation of credentials or of a true copy thereof will be determined by the date and time of the arrival of the head of the mission. Article 14 1. Heads of mission are divided into three classes, namely: (a) That of ambassadors or nuncios accredited to Heads of State, and other heads of mission of equivalent rank; (b) That of envoys, ministers and internuncios accredited to Heads of State; (c) That of chargés d’affaires accredited to Ministers for Foreign Affairs. 2. Except as concerns precedence and etiquette, there shall be no differentiation between heads of mission by reason of their class. Article 15 The class to which the heads of their missions are to be assigned shall be agreed between States. Article 16 1. Heads of mission shall take precedence in their respective classes in the order of the date and time of taking up their functions in accordance with article 13. 2. Alterations in the credentials of a head of mission not involving any change of class shall not affect his precedence. 3. This article is without prejudice to any practice accepted by the receiving State regarding the precedence of the representative of the Holy See. Article 17 The precedence of the members of the diplomatic staff of the mission shall be notified by the head of the mission to the Ministry for Foreign Affairs or such other ministry as may be agreed. Article 18 The procedure to be observed in each State for the reception of heads of mission shall be uniform in respect of each class. 6