290. Two or more Units may agree-
(a) that there shall be one Audit Department for that group of Units;
(b) that the Audit Department for a particular Unit shall serve the needs of the other Units party to the agreement, and any such agreement may contain such incidental consequential provisions as may appear necessary or desirable for giving effect to the purpose of the agreement and shall, in the case of an agreement that there shall be one common Audit Department, specify what Heads of the Units and the Legislature are to discharge the functions of the Head of the Unit with respect to the Audit Department.