Campbell Scientific Bowen Ratio Instrumentation - Manual (Page 19)

Section 2. Station Installation
2-9
If the LED is not already on, turn the potentiometer clockwise until it
turns on and then counter clockwise until it goes off.
Now, slowly turn the potentiometer clockwise until the LED comes on
again.
7. Return the switch to its normal operating position. The LED will turn off
several seconds after the switch is moved to the normal operating
position.
8. Set flag 4 low to write the time that site maintenance ended.
Cleaning the mirror with a cotton swab does not result in a surface condition
like the one reached after evaporation of a dew layer. Therefore, a more
appropriate bias adjustment is reached with a mirror surface on which a dew
layer has been formed and then evaporated.
By adding two steps to the above procedure, a more appropriate bias
adjustment can be made and the period between required mirror cleaning can
be further extended. These additional steps are:
9. Allow the system to run under normal operation for 8 to 24 hours, after
completing steps 1 through 8.
10. Now repeat step 1, 2, and 6 through 8.
FIGURE 2.7-1. DEW 10 Circuit Board