In addition to commands entered at the keyboard, either individually or via user defined functions, the tracking programs may also receive their command input from a disk file of command line images that are keyed to local sidereal or universal times of execution, and a disk file of untimed line images that are executed sequentially, as rapidly as the commands themselves will allow. In order to enter commands to the MODCOMP disk file, you must use the utility program CARD which is discussed in Chapter 5.