 Previously, music scheduling had been done by hand, as disc jockeys selected a song card from the front of a stack, played the track, and returned the card to the back of the stack to ensure that it was equally rotated with all available songs.With the use of computers, better decisions could be made based on a set of programmable rules.For instance, the rule of artist separation would ensure that two songs by the same artist needed to be separated by a given amount of time.