Casio 3476 Owner's Manual page 56

Illumination
The display of the watch is illuminated for easy reading in the dark. In any mode
(except when a setting screen is on the display), press B to illuminate the display for
about three seconds.
Illumination Precautions
• The LED that provides illumination loses power after very long use.
• Illumination may be hard to see when viewed under direct sunlight.
• Illumination turns off automatically whenever an alarm sounds or when time
calibration reception is in progress.
• Frequent use of illumination runs down the battery.
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