Navibe SP611 User Manual page 11

Reference
Button2
Action
LCD Backlight ON
LCD Backlight OFF
Button3
Action
Mode
Reset
3
Description
Press < 1 second, then LCD back light stays on
for 5 seconds. Press till the light is ON, then LCD
back light stays on permanently.
Press button again > 2 seconds, then LCD back
light OFF.
Description
press < 1 second: switch between MAX and AVG
speed.
press > 2 seconds: reset the distance, MAX and
AVG speed.