Canon A-1 Repair Manual page 66

The features of this mechanism are as follows:
1) Multiexposure is made possible with a camera
having a sprocket with only six teeth and in
which short stroke winding is possible.
Furthermore, short stroke winding is possible
even during windup after multiexposure has
been set.
2) As a clutch is constructed before the sprocket
and spool drive gear, it is not necessary to fix
the spool when multiexposure has been set.
(Contributes to decreasing the number of parts.)
3) The automatic reset mechanism eliminates worries
about forgetting to reset the camera after
multiexposure.
4) By setting the multiexposure, the wind stopper
is released. Therefore, even in AE discharge
condition after windup (EEEE EE) mark display),
AE recharge can be performed without wasting a
single frame.
67