Yamaha Electone EL-900 Owner's Manual page 156

NOTE:
Donﾕt use the Pitch Bend and Tempo at
the same time since you may inadvertently
apply both two controls at once.
10
156
Tempo Control
1 MODE
Determines the range of the Tempo control. Range: 1 - 12
The setting 2 (NARROW) results in a small amount of tempo variation
(70%-140%); the setting 12 (WIDE) results in a large amount of tempo
variation (50%-200%). (This control is the same as for Pitch Bend
above; the two cannot be used independently.)
3 TEMPO
On/off switch for control over the rhythm tempo. When on, pressing
the pedal with your toe speeds up the tempo; pressing it with your
heel slows it down. Releasing the pedal from either position causes it
to return to center, restoring the original tempo.