Canon SPEEDLITE EL-1 Advanced User's Manual page 51

2.
Set the flash exposure compensation amount.
Push the joystick to the left or right or turn <
compensation, and push the joystick vertically.
"0.3" indicates 1/3 stop and "0.7" indicates 2/3 stops.
To cancel flash exposure compensation, return the compensation
amount to "±0".
After changing the value, the changed value will be set even if you
push the joystick up and down.
After changing the value, the changed value will not be set if the <
button is pressed.
Note
Generally, set an increased exposure compensation for bright subjects and set a
decreased exposure compensation for dark subjects.
If the camera's exposure compensation is set in 1/2-stop increments, flash
exposure compensation will be up to ±3 stops in 1/2-stop increments.
When the flash exposure compensation is set on both the flash and the camera,
priority is given to the flash setting.
You can set the flash exposure compensation amount by turning <
without selecting < > with the joystick (C.Fn-13).
51
> to set the amount of
> directly
>