A few days left to GSSP. And last night, I could not guide with a better accuracy then 1.2 arc seconds RMS error - with all my efforts I could get easily below sub one arcsec accuracy. I have no idea what I did or changed. I hope that it was just the case of really bad polar alignment or such. Will try tonight, but this would suck for my imaging plans this weekend :-(
... I tried this tonight again. And I am almost convinced that this is because of the hot weather and the thermal disturbance during the night. I took a 10 min unguided exposure and it actually looked pretty good (my polar alignment was pretty good). I then observed the guide star in the PHD window and it jumped around (left, right, up, down - all directions) very quickly. I.e. it didn't look as if the guiding had issues. Well, keeping my fingers crossed!
And the next night it was even better. Some of the best guiding ever (0.6 arcsec combined RMS error)!