If more than 24 tracks of recording were required, it was possible in the mid-1970s and onwards with advanced servo-controlled machines to synchronize two (or more) 24-track recorders to behave as a single 48-track recorder (46 usable tracks due to the time code stripped on the first channel of each tape). Such precise synchronization was achieved by recording a time code on one of the tracks on each reel of tape: a computer system would keep the two time codes perfectly synchronized, and transparently as seen by the machine operator.