Originally posted by AstroDave The satellite orbits are continuously monitored and accounted for in the GPS broadcasts.
At the level we are concerned with, humidity has NO effect on astrotracer operations. It might cause your apparent camera position to be off by a few centimeters but that will have no effect on astrotracer operation. You would have to be mislocated by 10 to hundreds of meters before the sensor motion would not be adequate to stop star trails (assuming everything else was set up correctly - which seems to be the achilles heel of astrotracer operation!).
As an ending discovery, Rather than go through the motions they suggest to do a calibration, I racalled my phone has a compass, that requires me to do a figure eight held up to calibrate.
I did this with the k-3 for a few moments and got an OK. Not only that, I was able to track stars for 90 seconds with the 28mm, longest before that was 50 seconds.