From the manual (1987/1989, shared with the FX62 and FX65): "The ... FX60 chorus unit [is a] variable delay unit that gives the impression that more than one instrument is playing. It does this by delaying the sound of the instrument a small amount (4-6 milliseconds) and continuously varying the amount of delay ... [which] changes the pitch of the delayed signal. The delayed, slightly pitch shifted signal is mixed with the original signal and results in the chorus effect. ... The FX60 Stereo Chorus is a two-control knob chorus effect, offering adjustment of the sweep SPEED and DEPTH."