Furuno CH-37 - Manual (Page 16)

1-6
1.6 Background Color
The background color is available in deep blue, blue or black,
with the HUE key.
1.7 Degaussing the Screen
The screen is automatically degaussed at the interval selected
on the SYSTEM SETTING menu. However, when the picture
or picture color appears to be distorted, manually degauss the
screen with the DEGAUSS key.