[jase (Jason)]

All very sound advice by others, JohnG and Matt (g_day) in particular.
Simply training PEC while autoguiding is better than no PEC at all. If you’ve got a mount capable of PEC, you’d be foolish not to use it to extract maximum performance. Anything you can do to reduce the quantity of guiding corrections made by the auto-guider is a benefit. Each guiding correction is a chance for error such as over correction, troubled seeing etc.

As Matt highlights, the best possible way to record PEC is to perform multiple runs. A single run is one revolution of your worm/gear. If your mount supports it, you can record multiple runs and average them. This is something can be performed with the Gemini system. Most mounts only allow one PEC run.

By performing multiple runs, it is possible to eliminate seeing conditions influencing the result thus what you get is the raw PE of your mount. Software such as PEMPro will do multiple runs and analyse your data to produce a PEC curve which is then uploaded to your mount.. I’ve been using it for approx two years and swear by it. Version 2 now supports a polar alignment assistance tool which is quite handy.

As luck would have it, a few nights ago I used PEMPro to re-record PEC, so I’ve attached a few sample screen shots. The first image, shows the PE over 5 worm/gear revolutions - note the inconsistencies between each run (though there are some similarity between runs at ~1:20mins & ~4:40mins - total worm period is a bit over 5 mins for the Titan). The second is the PEC curve PEMPro recommends after the analysis. You can tweak this curve further if desired, but usually it’s sufficient as is. I’ve gone from a PE of +2.9/-2.3 down to +1.7/-1.5. I feel sure I could correct it better – considering I’m using a short focal length instrument (FSQ-530mm) to record this. For a wide field instrument, demands are considerably less. A longer focal length would obviously emphasise PE more. Ultimately, you should record the PEC curve at the focal length you’re imaging at or what ever is the longest instrument you have.

Happy to answer any questions you may have regarding PEMPro.

Note, PEMPro V2 now supports webcams for PE analysis.