Re: APPM 'BAD X SCALE' Error and Appropriate Troubleshooting?

Ray Gralak

Hi Greg,

If the image scale returned by the plate solve is more than a certain percentage away from the value you have set you will get that error message. The "Bad X scale" just happens to be checked before Y scale, so that's why you are seeing it. If X-scale is bad then Y-scale is also probably bad, but there is no reason to pop another error for it.

-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 Greg Vaughn
Sent: Thursday, January 2, 2020 12:52 PM
Subject: [ap-gto] APPM 'BAD X SCALE' Error and Appropriate Troubleshooting?

Happy New Year to everyone!

(Apologize in advance for the long post - but I've had to trim the log files significantly and I wanted to properly set
the stage with enough information to make the issue clear.)

Skies where I live were gorgeous last night and I set up my Mach 1 / AP 130 EDFGT (GTX focuser with field
flattener) with the idea of using some of the bells and whistles in APCC Pro I had not previously used, to improve
my imaging. In particular, I wanted to use APPM, with points customized for the azimuth and altitude that I give
me a clear shot of the sky on my back deck. (I set up and tear down each evening.) After some study and
watching Ray Gralak's presentation on YouTube to The Astro-Imaging Channel, I successfully used APPM with 20
points on Christmas Eve. However, an attempt with a similar set of points on Christmas night was unsuccessful.
On Christmas night, the connection with my camera (D810A) and the Platesolve2 through Sequence Generator
Pro were both successful, but while it appeared to generate successful solves (watching APPM 'run' dialog), it
would then slew slightly again and platesolve again, ultimately resulting in a RED status block saying 'Bad X Scale.'
This persisted through all of the points as it slewed and platesolved for each point. I had hoped that this was just a
case of an incorrectly entered image scale in Plate Solve Settings, but for my DSLR with essentially square pixels,
both X and Y arc-sec/pixel values were correct. Then I thought maybe the new information was being compared to
the successful run the evening before, unaware that I have a new setup each night. I unchecked all the calculated
model parameters (right hand side of APCC Pointing Model dialog page) in an attempt to clear the old model
(though the title in that block still lists the 24 DEC session as the model).
Last night I attempted to use APPM again, with a selection of 25 east model points within my field of view. This
time I performed a 'Solve and sync' in SGP first, then moved to APPM for the run with the 25 points. Unfortunately
I had the same experience again. I aborted and started it again twice when the first point registered the red 'BAD X
SCALE' in the status block.

So, a few questions:

1. What generates a 'BAD X SCALE' error in APPM? (Has anyone seen this and how did you correct it?)
2. Do I need to 'flush' the model generated by APPM between imaging sessions if I setup and take down my
equipment each imaging session? (I think the answer is yes.)
3. What is the proper way to 'flush' the model before starting APPM in those subsequent sessions (if required)?

I talked briefly with George at AP today and in the course of that discussion it dawned on me that the camera may
have taken a 5second exposure at 200 iso instead of the 6400 iso or 12800 iso that I usually have set for use on
platesolving in SGP. (I normally specify iso 200 and 5min for most of my individual light frames in SGP, however.)

I'm sure this is something very basic that I'm doing wrong, but not sure what. A very trimmed down version of the
APCC logs are attached.

If anyone has some thoughts or experiences here to share, that would be very helpful.

Thanks in advance and all the best for clear skies and a prosperous 2020!


p.s. Not familiar with the logs yet. If the answer is there, don't assume I know exactly where to look.

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