 The line printer employed a series of status codes, specifically "ready", "online", and "check".If the "online" status was set to "off" and the "check" status was set to "on," the operating system would interpret this as the printer running out of paper.However, if the "online" code was set to "on" and the "check" code was also set to "on", it meant that the printer still had paper, but was suffering an error (and may still be attempting to run).