Humminbird Dimension 3 Operation Manual page 24

To select a unit of measurement, press the SELECT button until the box before UNITS is blacked
in. Then, press the Up or Down arrow to select the unit to change. Press ON-OFF until the unit you want is
displayed.
To adjust the contrast of the Dimension 3 display, press the SELECT button until the box before
CONTRAST is blacked in. Then, press the Up or Down arrow until the screen shows the desired degree of
contrast.
When you are finished with the Custom Program screen, press the SCREEN key to return to
normal Dimension 3 operation.