Re: APPC refraction correction question

Ray Gralak

Can anyone, who is using APPM to build DEC ARC models,
First, you are not creating "DEC ARC" models because that version of APCC has not been released. You are creating a full-sky model based on a limited area of the sky.

Second, unchecking/checking any option will re-calculate the best-fit values from the supplied data. "Best-Fit" depends on the quality of the data and how the model terms match the mechanicals. If you have a scope with unmodeled behavior then the terms can vary significantly.

-Ray Gralak
Author of APCC (Astro-Physics Command Center):
Author of PEMPro V3:
Author of Astro-Physics V2 ASCOM Driver:

-----Original Message-----
From: [] On Behalf Of Craig Young
Sent: Thursday, July 30, 2020 5:38 PM
Subject: Re: [ap-gto] APPC refraction correction question

Can anyone, who is using APPM to build DEC ARC models, confirm that enabling refraction correction changes
the model terms significantly. You can easily run this test during the day by slewing to any location in the sky and
toggling the state of the refraction correction checkbox and noting the change in the Offset Error-Hour Angle term,
located at the top of the model terms list.

I am trying to find out if this is an error in APCC or something in my system. As discovered above, if I remove the
Offset Error term when refraction correction is enabled, then the tracking rates look reasonable. But I am not sure if
refraction correction is now accurate when removing the model term. I thought I would check with others before
reporting this formally as a software error in APCC.


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