Canon EOS-1 DX Mark III Advanced User's Manual page 178

2.
Set the desired minimum shutter speed.
Automatically set
If you select [Auto], turn the <
to standard speed (toward Slower or Faster), then press <
Manually set
If you select [Manual], turn the <
then press <
Caution
If a correct exposure cannot be obtained with the maximum ISO speed limit set
with [Auto range], a shutter speed slower than the [Min. shutter spd.] will be set
to obtain the standard exposure.
This function will not be applied to flash photography.
Note
When [Auto(Standard)] is set, the minimum shutter speed will be the reciprocal of
the lens focal length. A single step from [Slower] to [Faster] is equivalent to a
single stop of the shutter speed.
>.
178
> dial to set the difference relative
> dial to select the shutter speed,
>.