(a) a post is vacant; or

(b) a substantive holder of a post is temporarily absent on leave or temporarily incapacitated through illness or for any other cause from the performance of his duties,

an officer may be appointed to act in such post or be required to cover the duties of such post in addition to his own and be eligible for payment of an acting allowance or a charge allowance at the rates and in accordance with the terms and conditions as set out in the Seventh Schedule.

Seventh Schedule: