[glend (Glen)]

I have owned my SQM for maybe 10 years, and have used it on all my dark site trips, and it still gets used from my backyard observatory to track light pollution levels over the years, and discriminate between good and great nights. It also surprisingly correlates well with the reading on the global light pollution map section for Australia.

As far as aiming goes, I am always pointing it straight up, for the sky should be darkest at the zenith ( the atmosphere is thinnest straight up), and most of my imaging is done at elevations above 60 degrees.

There are some seasonal factors that affect readings, for example the Milky Way overhead on a perfect night will yield a lower SQM reading than a night when it is rotated out of view ( assuming your somewhere that is actually reasonably dark enough to see the Milky Way in all its glory).

Regarding cloud, obviously cloud is bad, even cloud in the distance can reflect back ground light. Also there are times you may think there is no cloud but high misty cirrus maybe present, and affect your reading. This is why it is important to keep a record of your reading by site, so you immeadiately know based on the history, what your dealing with.

As far as the Seeing debate goes, a SQM reading is just one indicator, and the value displayed can not be taken alone. Often upper winds, thermal inversions, etc can affect imaging significantly. An experienced user, with a site history log, can make assumptions about upper atmo Seeing, but there is no substitute to actually looking with your scope to confirm Seeing.

I also remove the battery when it is stored, and there are many posts on forums, like Cloudy Nights, where they discuss batteries affecting readings. If you ask your question on Cloudy Nights you will get heaps of responses, and opinions (not all based on experience).

If for nothing else, it will allow you to benchmark all your dark site trips, and occasionally settle arguments about what site is darker. Have fun.