Canon AE-1 - Manual (Page 34)

Checking Film Winding
Operate the film advance lever while
watching the film rewind knob. If it rotates,
the film is properly loaded. If the rewind
knob does not rotate, open the back cover
and load the film again from the start.
6 Setting the ASA Film Speed
After loading the film, set the ASA film
speed according to the ASA speed of the film
in use. To set the ASA, first push the film
advance lever out to its 30° stand-off position
away from the camera body, then lift up the
ASA ring around the shutter dial and rotate it
in either direction until the proper number is
aligned with the green index mark. ASA is a
numerical rating of a film's sensitivity to light.
A higher ASA number indicates a faster film
which is more sensitive to light. On the other
hand, a lower ASA number indicates a slower
film which is less sensitive to light. The ASA
rating recommended by the manufacturer is
printed on the film box, e.g., ASA 100.