The nomenclature of the Erhardt-Perkins system is also very different from the Ernie Zampese-Don Coryell "Air Coryell" timed system. Route patterns of the receivers are numbered instead of named in the Air Coryell system (thereby making memorization easier). For example, an Air Coryell play such as "924 F stop swing" indicates that the primary wide receiver (X) should run a 9 pattern (a go), the tight end (Y) should run a 2 pattern (a slant), the secondary wide receiver (Z) should run a 4 pattern (a curl) and the F-back should go out for a swing pass (see Offensive nomenclature). Timing and precision are extremely important under the Air Coryell system, as the routes are intended to run like successive clockwork in order to be successful.