I was all set to do some imaging last night. Beautiful, clear, cool day. Got focused and calibrated for a new target, took a dark and started imaging. Got 15 minutes into a 20 minute sub and it clouded over!! Aaarrggh!
Anyway, I thought I'd have a look at the PE for my mount in between the clouds.
Here's the result - not bad really, inside what Tak specifies for the EM-400 (+-3.5 arcsec)
http://www.pbase.com/gailmarc/image/93621871
(Note: Data gathered by autoguiding in CCDSoft with corrections disabled)