Simrad AP28 Operator's Manual page 59

For data types which can be calibrated, an overlay screen
displaying the data from the selected data source will
appear first (Ref. Installation/Calibration).
Display
The display is controlled by the Contrast setting and two
user profiles that can be individually adjusted.
For each profile you can:
-
-
-
See information about the selected
data source.
Enter the Calibrate and Offset
menu.
(Ref. Installation/Calibration).
Proceed to display a list of
available sources for the given
data type.
Adjust light level
Adjust the light color
Invert the display
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