7-Z0444 is a companion number to the other requirements of the same series issued by the Italian manufacturer, and the two are often called up together in an engineering specification so that between them they cover the classes of component used on a vehicle programme. Reading a family of requirements of this kind is a task in itself: the numbers are issued to cover equipment as it appeared, so a programme that introduces a new class of device may be covered by an existing number, by an amendment to it, or by a new number issued for the purpose, and the engineering specification is what establishes which applies. A supplier's first action should therefore be to obtain the specification and the numbers it invokes rather than to assume that a familiar number still governs the work.