Leica MX400 Operating Instructions Manual page 189

Operator's Manual
The receiver will go on to conduct a Contrast test. Observe that the
display goes through its full range of contrast from white to black.
Press OK if it varies correctly or Fail if it doesn't. Next, the receiver
will conduct a Backlight test. Observe that the display goes through
its full range of illumination. Press OK if it varies correctly or Fail
if it doesn't.
Then, the receiver will conduct a Keylight test. You may need to
dim the lights in the room or shade the keyboard so that you can see
the backlights behind the function and softkeys. Observe that the
keypad backlights go through their full range of illumination. Press
OK if it varies correctly or Fail if it doesn't.
Upon completion of the above tests, a Test Results screen will be
displayed. In addition to the visual tests which you witnessed, the
receiver also performs background tests on the digital GPS receiver
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Appendix C - Engineering Mode
Version 3.3