Hi Steve,
I had been assuming I could use measurements from multiple nights. I should devote a few nights to model this correctly.

I've not tried yet, but are you saying I can use the TC wizard to do the measurements. I assumed that as the ATLAS cannot do it that it wouldn't work. It's too windy tonight to try which is a shame.

I did find this script:

http://www.russels-astro.com/ftp/focus.vbs

on Russel's blog (http://www.russels-astro.com/blog/?p=178) which seems to do exactly what I want. He suggests running this automatically at the end of each image acquired by Maxim. Bob, could ACP support a similar script?

To do this accurately I'll need to get some external sensors. Another job for the projects list