Text in force at CS23-6: from CS23-5, effective 15 Aug 2017.
(a) Each aeroplane must display in a conspicuous manner any placard and instrument marking necessary for operation.
(b) The design must clearly indicate the function of each cockpit control, other than primary flight controls.
(c) The applicant must include instrument marking and placard information in the Aeroplane Flight Manual.
ED Decision 2017/013/R · Source