It is relatively easy to measure the sky background level with an astroimaging setup accurately. It can be then used to calibrate the sky brightness sensor.
You need to have:
– setup with a monochromatic camera and luminance filter
– proper software – for example ASTAP
First, download and install ASTAP software and star database (H17 is okay) https://www.hnsky.org/astap.htm .
Then take 15-60 seconds shot with a camera and L filter.
Open the file in ASTAP software.
Solve it (press Solve button).
Select Tools -> SQM Measurement. The only value you need to enter is the pedestal – that is the mean value of the corresponding dark frame. The SQM value is displayed directly: