A 60Hz sine wave is recorded on one track of a tape which is used for motion picture sound recording, generated when the film is being shot, thus the frequency is an accurate measure of the camera speed. The pilot is then used later to synchronize the tape playback to the picture action, allowing movie sound to be recorded independently of the film, as double system sound. However, with a pilot tone, although the slave can syncphase lock with the master, the slave has no way of knowing where in the program the material the master tape is, and so is severely limited as a synchronization tool. The same is true for speed-only sync codes such as FSK and DIN sync. See neo-pilot, control track, reference frequency.