a system, it was common practice to skip numbers for the rungs to allow later additions as required.

When the rack was manufactured, as a wire was installed, each end would be marked with wire labels (a.k.a. wire markers). This also applied for pulling wire into the factory through conduit or in trays where each wire would have corresponding numbers. Wire labels were typically pieces of white tape with numbers or letters printed onto them and collected in small, pocket sized booklets. A number strip would be peeled out and wrapped around