Juniper Allegro CE Owner's Manual page 76

The Backlight tab allows you to select the length of time you want the
backlight to remain on while the Allegro is in an idle state and to set
the brightness of the backlight.
The Options tab is used to set the display heater. The options are Auto
and Off. Auto is the default setting and turns the heater on
automatically when the temperature is -3° C or less. You can adjust
the display contrast by moving the slide bar left or right.
❖ Note: If you are using alkaline batteries, the display heater cannot be
used. The Auto option is not available.
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