Article 26 was significantly influenced and inspired by the corresponding article of the 1976 UNCITRAL Arbitration Rules (article 27) and indeed the wording of both articles is very similar. The first drafts of article 26 hewed even more closely to article 27 of the UNCITRAL Arbitration Rules, with only minor differences between them. Article 26 started to take its own form by introducing the principle that the ability of the tribunal to appoint an expert was subject to the contrary agreement of the parties. This reflected the prevailing view arising from the Working Group’s early discussions that parties should be able to preclude the tribunal from calling an expert at any time; this issue was to be distinguished from the question of whether a party could present the evidence of an expert witness, and it was agreed that the arbitral tribunal should hear such expert witnesses as provided for in the UNCITRAL Arbitration Rules.