Thanks. Initial measurements suggest that the actual precision is around 3.5mmag. Seeing was so bad that the aperture is 12 pixels in radius, and at 1.4arcsec/pixel that corresponds to a disk half a minute across! FWHM is markedly smaller, of course, but still far too big. Perhaps observing in Sloan-r might be an improvement.
It’s even windier today and I’ve serious doubts whether it’s worth even opening the dome. Incidentally, the gusts last night were strong enough to make the scope flap around beyond the ability of the autoguider to track correctly when observing at low altitude late in the session. I lost around 5% of the data to that cause.