The purpose of this SAE Aerospace Recommended Practice (ARP) is to provide recommendations for marking wire and cable insulations to meet legibility requirements. This information is generic and applies to any type of wire marking system, such as an ultraviolet (UV) laser marking system or an inkjet or other ink based wire marking system. This ARP is limited to the legibility of human-readable characters and does not address bar code or other machine-readable symbols. In this ARP, the term wire refers to jacketed cables and fiber optic cables in addition to individual wires. This ARP defines the factors that affect the legibility of markings on wiring. Two generic types of variables affect legibility: stimulus variables and environmental variables. Stimulus variables are those factors involving the mark itself. This ARP establishes a set of guidelines for key stimulus variables that contribute to legibility and which should be taken into consideration in the course of specifying and using wire marking equipment. Environmental variables affect the reading of the marking, for example lighting, observer-stimulus distance, orientation of observer to stimulus, clutter, visual acuity of observer, state of mind, and visual exposure duration. The marking of electrical wires and cables and fiber optic cables with their unique identification codes is a critical manufacturing function to enable production and maintenance personnel to easily identify each wire and cable. The ability of personnel to read the codes is highly dependant upon the legibility of the markings. This is especially important on smaller single core wires where the wire diameter limits the dimensions of the characters making up the code. This ARP has been established to make recommendations on the ergonomic factors that equipment manufacturers should follow when designing wire marking equipment for use in wire harness production to help maximise the legibility of the codes.