Canon SPEEDLITE EL-1 Advanced User's Manual page 85

3.
Set the same ISO speed as on the camera.
Push the joystick vertically.
Push the joystick up / down / left / right or turn < > to select item (1),
then push the joystick vertically.
Push the joystick to the left or right or turn < > to set the ISO speed,
then push the joystick vertically.
The ISO speed can be set within a range of ISO 25 to ISO 819200, in
1/3 increments.
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