Canon A-1 - Manual (Page 47)

Check to see that the cartridge is in a
fully-seated position and that the film is
taut. If there is film slack, gently turn the
rewind crank clockwise until it stops. Snap
the back cover shut. Gently turn the rewind
crank in the direction of the arrow to take
up film slack and then fold the rewind crank
back in.
Switch the AE mode selector to Tv and turn
the AT dial to a fast shutter speed. Now
make two blank shots, turning the film
advance lever and releasing the shutter, so
that the frame counter advances from “S” to
“0". While doing this, keep an eye on the
rewind knob. If it rotates, the film is
properly loaded. If it does not rotate,
chances are that the film is sagging or the
film perforations are not properly engaged in
the
take-up spool and film transport
sprocket. If the rewind knob still does not
rotate once you have gently turned the
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