Canon EOS 1D Software Instruction Manual page 196

Personal Function Settings
Illuminates the LCD panel during bulb exposures
After the bulb exposure starts, press the <LCD panel illumination> button to illuminate the
LCD panel until the bulb exposure ends.
Convenient when you want to monitor the elapsed bulb exposure time.
Taking bulb shots for long periods speeds up battery charge depletion and reduces the
number of available shots.
Sets the default settings when the CLEAR button is ON
You can use this function to select the default mode selected when you press the CLEAR
button <QUALITY+WB>.
Convenient when you want to instantly switch to frequently-used settings.
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