During my session, I noticed an issue with calculating RMS. I used PHD2 for guiding, and I use the Z-filter algorithm for DEC control. According to the folks at PHD2, when Z-filter is used, PHD2 shifts the image - RA is centered, but DEC is shifted by 1 arc-second. I'm not sure why, but this will throw off the calculation of RMS due to the DEC shift. Take a look at the attached pictures so you can see what I mean.

But very nice tool!

Regards,

jmh

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