That's correct.  Unlike many other mount brands, iOptron PEC handling fiercely fights with mount guide inputs.   I've tried it a dozen times on three different mounts with the internal guider and PHD2 and the result was clear each time: if you're guiding an iOptron mount, do not use mount-based PEC.  My results were always noticeably worse, and often were disastrous.  

The thing is, none of my iOptron mounts have anything but smooth PE... and smooth PE is easy to guide out. 

Predictive PEC in PHD2 or GPG RA Guiding in KStars work great, though.  Just find the worm period of your mount and specify it in the software vs letting the software "guess" at your worm period.

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