Date   

Re: Adjust CP4 Clock Frequency

Craig Young
 

Ray,
So if I understand correctly, using your scope, unguided, and with APCC corrective tracking, you can plate solve your first image, three hours later plate solve your last image and the difference in plate solutions is less than 1 arc-sec?

Craig


Re: Adjust CP4 Clock Frequency

Ray Gralak
 

On the other hand, if you are working on improvements to an unguided solution and need a test site I would be
glad to help. ATrack is both a correction tool but also an analysis tool. Because it gives you the exact tracking
rates required for unguided imaging, you can compare the values with a modeled approach and see where the
problems are. The goal of the model should be to provide tracking as good as ATrack or an autoguider.
But why? Using APCC Pro's modeling I have had no problem doing 20-30 minute images unguided at 1.74 arc-sec/pixel with round stars. I've posted maybe about a dozen here before. A number of users have also done unguided images.

Some scopes need closed loop guiding because they are hard to model. I think yours is one of them.

Even the concept of using drift to set the tracking rate was done long ago. My own PulseGuide did something similar over 15 years ago. You would center a star, start a timer and let the star drift. The user would re-center the star and click another button andPulseguide would set the tracking rate in both declination and right ascension. It could be used for any object too, like comets.

And what might be even more crazy is that PulseGuide could do this *before* custom tracking rates could be set in the AP control boxes. It did this by sending evenly spaced, well-timed guider pulses, thus its name, "PulseGuide". You can still download it from here: https://www.pulseguide.com.

And it's not like I don't have experience with lots of telescopes, from refractors, SCTs, MakCass's, Newts, RC's, etc. I've experience with scopes with serious flexure issues that can make dramatic changes in focus as temperature swings, like my old18-inch Newt on a 1200GTO circa 2003 (and a younger me! :-)

https://raygralak.smugmug.com/Astronomy/18-CPT/

For now, APCC hasn't been able to do miracles with your particular truss tube scope so it's necessary for you to do closed loop autoguiding. For people with solid, repeatably pointing scopes APCC Pro's tracking rate correction already sets the tracking rate well enough to do unguided imaging, and even to dither without having to do plate solves. :-)

-Ray Gralak
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of PEMPro V3: https://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Craig Young
Sent: Tuesday, May 5, 2020 7:49 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

Ray,
No problem, let me know if you want to discuss further offline.

But as I said above, it is not really necessary because ATrack provides excellent tracking with whatever condition
the scope/mount are in. APCC tracking is not that robust, it blindly sets the tracking rate, based on a model, with
no feedback. Given any factors not accounted for accurately in the model you should not expect a perfect
tracking solution. Both ATrack and autoguiders use feedback to correct tracking rates. So rather than try to
research the source of the tracking error it is a lot simpler to let ATrack or an autoguider correct for it and not use
a tracking model.

On the other hand, if you are working on improvements to an unguided solution and need a test site I would be
glad to help. ATrack is both a correction tool but also an analysis tool. Because it gives you the exact tracking
rates required for unguided imaging, you can compare the values with a modeled approach and see where the
problems are. The goal of the model should be to provide tracking as good as ATrack or an autoguider. The
problem with an autoguider is it doesn't tell you what the tracking rates should be .. ATrack provides that.

But hopefully a model solution will be coming, and from what I have heard over the last year, it might be coming
from AP. Looking forward to it.

Craig


Re: need learning aids for astrophoto

 

>>> Some of the newer DSLRs have very low noise.  Read up on the new Canon Ra, about which Sky& Telescope and Astronomy are raving.  That said, the cooling available in many astro cameras is an advantage.

The Canon RA is $2500

you could get a very nice cooled astronomy camera for that price. shoot, you could get a very nice cooled astronomy camera for less than 1/2 that price

it's a nice camera for sure. I think it's more geared for casual astronomy users who also want to shoot terrestrial and maybe already own some canon glass. If i were starting from scratch and focused on astronomy, i don't think this direction would be my first choice.

Brian

On Tue, May 5, 2020 at 8:24 PM Worsel via groups.io <bryancashion=yahoo.com@groups.io> wrote:
I agree with Mike that a DSLR is a good option to consider.  I would offer a different take on the following.

2. IMO a DSLR is a good choice if you're just starting out. But I think buying a cooled CMOS astronomy camera is a better choice if your budget allows. Consider:

A) A CMOS camera is powered from the USB (usually USB 3.0) cable, not from an internal battery that might not last through an imaging session.

I power my DSLRs with the AC adapter, not a battery.  This works in an observatory, off 120VAC (mains) or the field, if you have a large capacity (amp-hours) battery and inverter

B) A cooled CMOS camera has lower noise than an uncooled DSLR.

Some of the newer DSLRs have very low noise.  Read up on the new Canon Ra, about which Sky& Telescope and Astronomy are raving.  That said, the cooling available in many astro cameras is an advantage.

C) ZWO offers an off-axis guider (OAG) that mounts in between the OTA and the imaging camera. A small lightweight (and inexpensive) camera screws into this OAG. You can easily add autoguiding without needing a separate guide scope and camera. (I use a separate guider for specific reasons related to my imaging goals.)

I image with an Astrodon MOAG, which sits between the camera and the scope, and a DSLR.


Bryan



--
Brian 



Brian Valente


Re: need learning aids for astrophoto

Worsel
 

I agree with Mike that a DSLR is a good option to consider.  I would offer a different take on the following.

2. IMO a DSLR is a good choice if you're just starting out. But I think buying a cooled CMOS astronomy camera is a better choice if your budget allows. Consider:

A) A CMOS camera is powered from the USB (usually USB 3.0) cable, not from an internal battery that might not last through an imaging session.

I power my DSLRs with the AC adapter, not a battery.  This works in an observatory, off 120VAC (mains) or the field, if you have a large capacity (amp-hours) battery and inverter

B) A cooled CMOS camera has lower noise than an uncooled DSLR.

Some of the newer DSLRs have very low noise.  Read up on the new Canon Ra, about which Sky& Telescope and Astronomy are raving.  That said, the cooling available in many astro cameras is an advantage.

C) ZWO offers an off-axis guider (OAG) that mounts in between the OTA and the imaging camera. A small lightweight (and inexpensive) camera screws into this OAG. You can easily add autoguiding without needing a separate guide scope and camera. (I use a separate guider for specific reasons related to my imaging goals.)

I image with an Astrodon MOAG, which sits between the camera and the scope, and a DSLR.


Bryan


Re: Adjust CP4 Clock Frequency

Craig Young
 

Ray,
No problem, let me know if you want to discuss further offline.

But as I said above, it is not really necessary because ATrack provides excellent tracking with whatever condition the scope/mount are in.  APCC tracking is not that robust, it blindly sets the tracking rate, based on a model, with no feedback.  Given any factors not accounted for accurately in the model you should not expect a perfect tracking solution.  Both ATrack and autoguiders use feedback to correct tracking rates.  So rather than try to research the source of the tracking error it is a lot simpler to let ATrack or an autoguider correct for it and not use a tracking model.

On the other hand, if you are working on improvements to an unguided solution and need a test site I would be glad to help.  ATrack is both a correction tool but also an analysis tool.  Because it gives you the exact tracking rates required for unguided imaging, you can compare the values with a modeled approach and see where the problems are.  The goal of the model should be to provide tracking as good as ATrack or an autoguider.  The problem with an autoguider is it doesn't tell you what the tracking rates should be .. ATrack provides that.

But hopefully a model solution will be coming, and from what I have heard over the last year, it might be coming from AP.  Looking forward to it.

Craig


Re: Adjust CP4 Clock Frequency

Ray Gralak
 

Craig,

So Atrack is essentially an autoguiding program. It's been done before in many different ways. Closed loop guiding is usually more accurate, so nothing new here. Wait for machine learning though and you will see improvements without closed loop responses.

-Ray Gralak
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of PEMPro V3: https://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Craig Young
Sent: Tuesday, May 5, 2020 7:31 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

Roland,
I do agree with you that errors in polar alignment, tube flexure, mirror shift, cables, etc can all contribute to factors
that will reduce the effectiveness of using APCC for long duration unguided imaging on larger SCTs. I have seen
this also on Parmount mounts where ATrack is used to correct tracking over long periods of time, so it is not just
an AP problem. ATrack doesn't really care if the sidereal tracking rate is wrong or polar alignment or any other
problem with the system, it is similar to using an autoguider which also corrects tracking, but in a different way. So
there is no real need to try and diagnose the system when it is not really needed.

It is best to simply accept the limitations of the system, which includes the mount, the optical train, the pier and
foundation, sky conditions, etc and just plan to use an autoguider or a program like ATrack.

Craig


Re: Adjust CP4 Clock Frequency

Ray Gralak
 

Craig,

Nothing indicates an error in mount clock rate.

As I said before the tracking rate errors you are seeing in the APCC version you are using are almost certainly caused by unmodeled pointing errors in your truss tube OTA. There is a solution coming using a combination of temperature modeled pointing terms and machine learning.

No matter what the temperature is .. a warm summer night or a cold winter night .. the tracking
corrections are always the same.
Refraction and flexure changes caused by temperature don't affect tracking? I suppose your focus never shifts either with temperature?

Why don't we take this offline?

-Ray Gralak
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of PEMPro V3: https://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver


-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Craig Young
Sent: Tuesday, May 5, 2020 7:08 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

ATrack monitors a science images folder for new images recorded by the camera. New images are added by
Voyager/MaximDL. When a new image is detected ATrack does a plate solve and measure both drift (difference
between last image and this image) and shift (difference between a reference position or image and this image).
The drift is then used to adjust the tracking rate, the shift is used to temporarily change the motor speed for a
period of time to recenter the next image. Through an observing run of several hours ATrack will change the
tracking rate (RA, DEC) to minimize the drift rate and keep the image centered. It does this very accurately.
ATrack does not care what the cause of the drift, it simply measures it and readjusts the motor speeds to cancel it.
Through the night the changes are very small and consistent .. there is no wild jumps. It is also very repeatable,
from night to night. No matter what the temperature is .. a warm summer night or a cold winter night .. the tracking
corrections are always the same.

Now, if I turn off tracking correction on ATrack and turn on tracking correction in APCC then the stars drift away
very quickly .. pixels per minute .. about 1 arc sec a minute. This happens whether I use a 25 point model or a 200
point model. When I compare the correction rates in APCC with ATrack I see the same difference no matter
where I am pointed. East side or West side. The mount is always tracking in RA too fast and has to be slowed
down. This is consistent with ATrack which always shows the mount tracking too fast and it uses correction
values that are negative .. in other words, it tries to slow down the sidereal tracking rate.

The fact that DEC is similar would seem to indicate there is a base constant in the motor speeds that is incorrect.
DEC is always a positive number in the range 0.02000 to 0.01200 arcsec/sec and is the same in both East and
West sides.

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

Roland,
I do agree with you that errors in polar alignment, tube flexure, mirror shift, cables, etc can all contribute to factors that will reduce the effectiveness of using APCC for long duration unguided imaging on larger SCTs.  I have seen this also on Parmount mounts where ATrack is used to correct tracking over long periods of time, so it is not just an AP problem.  ATrack doesn't really care if the sidereal tracking rate is wrong or polar alignment or any other problem with the system, it is similar to using an autoguider which also corrects tracking, but in a different way.  So there is no real need to try and diagnose the system when it is not really needed.

It is best to simply accept the limitations of the system, which includes the mount, the optical train, the pier and foundation, sky conditions, etc and just plan to use an autoguider or a program like ATrack.

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

ATrack monitors a science images folder for new images recorded by the camera.  New images are added by Voyager/MaximDL.  When a new image is detected ATrack does a plate solve and measure both drift (difference between last image and this image) and shift (difference between a reference position or image and this image).  The drift is then used to adjust the tracking rate, the shift is used to temporarily change the motor speed for a period of time to recenter the next image.  Through an observing run of several hours ATrack will change the tracking rate (RA, DEC) to minimize the drift rate and keep the image centered.  It does this very accurately.  ATrack does not care what the cause of the drift, it simply measures it and readjusts the motor speeds to cancel it.  Through the night the changes are very small and consistent .. there is no wild jumps.  It is also very repeatable, from night to night.  No matter what the temperature is .. a warm summer night or a cold winter night .. the tracking corrections are always the same.

Now, if I turn off tracking correction on ATrack and turn on tracking correction in APCC then the stars drift away very quickly .. pixels per minute .. about 1 arc sec a minute.  This happens whether I use a 25 point model or a 200 point model.  When I compare the correction rates in APCC with ATrack I see the same difference no matter where I am pointed.  East side or West side.  The mount is always tracking in RA too fast and has to be slowed down.  This is consistent with ATrack which always shows the mount tracking too fast and it uses correction values that are negative .. in other words, it tries to slow down the sidereal tracking rate.

The fact that DEC is similar would seem to indicate there is a base constant in the motor speeds that is incorrect.  DEC is always a positive number in the range 0.02000 to 0.01200 arcsec/sec and is the same in both East and West sides.

Craig


Re: Adjust CP4 Clock Frequency

Roland Christen
 

Please do the test that I asked and we'll go from there.

Roland



-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Tue, May 5, 2020 8:14 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

Dale,
Good point, I would like to continue investigating the discrepancy.  To me some diagnostics are needed and I am asking if AP would add them to the AE tab.

Craig


Re: Adjust CP4 Clock Frequency

Roland Christen
 


But that appears to be asking too much,
The software for that is not presently available in APCC. We have it here for internal testing, but never will it be available for general use and pirating by our overseas competition.

Roland


-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Tue, May 5, 2020 8:07 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

I don't think it is a coincidence Ray.  But it is easier to make that statement than to try and find the real problem.  Notice that it could easily be determined if we had a feature in APCC AE tab to run some diagnostics on the encoder and tracking.  But that appears to be asking too much, so it is simpler to try and explain it away.  What is the harm in adding some diagnostics?  Seems like a professional mount like the 1600 would give the user some additional tools to fine tune it.  Or is this too complex for us amateurs and should only be left to the hands of experienced engineers?

Craig


Re: Adjust CP4 Clock Frequency

Roland Christen
 

Or C you are not polar aligned or D you have differential flex which I have seen in the larger SCTs in fact of this magnitude and more.
It is virtually impossible for the encoder to have such large errors- your error is off by 100x. I just ran a test of a random encoder mount, tracking at sidereal, counting pulses from a Renishaw encoder over time. The tracking rate is constant over a 30 minute period of less than 0.2 arc seconds. I then changed the tracking rate by 0.1% and recorded the error - I can upload an image showing the result if you don't believe it.

Roland Christen


-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Tue, May 5, 2020 7:33 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

I disagree Ray that this is the more likely reason.  If it were the reason then I would see a divergence between ATrack and APCC.  I don't, they follow each other in parallel which means there is a constant factor that is causing the difference.  The two likely constants are: a) the sidereal rate is not sidereal, or b) the encoder, if used to determine sidereal rate, is not calibrated.

Craig


Re: Adjust CP4 Clock Frequency

Ray Gralak
 

Craig,

Say there is a tracking rate error of 0.1%. What makes your software immune to this tracking rate error? That is do you have to adjust the calculated rate you get by 0.1%?

-Ray Gralak
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of PEMPro V3: https://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Craig Young
Sent: Tuesday, May 5, 2020 6:14 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

Dale,
Good point, I would like to continue investigating the discrepancy. To me some diagnostics are needed and I am
asking if AP would add them to the AE tab.

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

Dale,
Good point, I would like to continue investigating the discrepancy.  To me some diagnostics are needed and I am asking if AP would add them to the AE tab.

Craig


Re: Adjust CP4 Clock Frequency

Dale Ghent
 

On May 5, 2020, at 9:07 PM, Craig Young <craig.young.m8@...> wrote:

I don't think it is a coincidence Ray. But it is easier to make that statement than to try and find the real problem. Notice that it could easily be determined if we had a feature in APCC AE tab to run some diagnostics on the encoder and tracking. But that appears to be asking too much, so it is simpler to try and explain it away. What is the harm in adding some diagnostics? Seems like a professional mount like the 1600 would give the user some additional tools to fine tune it. Or is this too complex for us amateurs and should only be left to the hands of experienced engineers?
Yo, just a bystander watching an otherwise quite technical thread here, but check the tone before proceeding. You're either investigating a discrepancy and its cause, or you're trying to accuse people of things with a chip on your shoulder. Pick one.

Thanks
/dale


Re: Adjust CP4 Clock Frequency

Craig Young
 

I don't think it is a coincidence Ray.  But it is easier to make that statement than to try and find the real problem.  Notice that it could easily be determined if we had a feature in APCC AE tab to run some diagnostics on the encoder and tracking.  But that appears to be asking too much, so it is simpler to try and explain it away.  What is the harm in adding some diagnostics?  Seems like a professional mount like the 1600 would give the user some additional tools to fine tune it.  Or is this too complex for us amateurs and should only be left to the hands of experienced engineers?

Craig


Re: Adjust CP4 Clock Frequency

Ray Gralak
 

I disagree Ray that this is the more likely reason. If it were the reason then I would see a divergence between
ATrack and APCC. I don't, they follow each other in parallel which means there is a constant factor that is causing
the difference. The two likely constants are: a) the sidereal rate is not sidereal, or b) the encoder, if used to
determine sidereal rate, is not calibrated.
That doesn't prove anything. That coincidence could be accounted for by many things, including different refraction calculations.

I am certain that the version of APCC you are using doesn't account for changes in modeling parameters because of temperature.

-Ray Gralak
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of PEMPro V3: https://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver


-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Craig Young
Sent: Tuesday, May 5, 2020 5:34 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

I disagree Ray that this is the more likely reason. If it were the reason then I would see a divergence between
ATrack and APCC. I don't, they follow each other in parallel which means there is a constant factor that is causing
the difference. The two likely constants are: a) the sidereal rate is not sidereal, or b) the encoder, if used to
determine sidereal rate, is not calibrated.

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

I disagree Ray that this is the more likely reason.  If it were the reason then I would see a divergence between ATrack and APCC.  I don't, they follow each other in parallel which means there is a constant factor that is causing the difference.  The two likely constants are: a) the sidereal rate is not sidereal, or b) the encoder, if used to determine sidereal rate, is not calibrated.

Craig


Re: Adjust CP4 Clock Frequency

Ray Gralak
 

With ATRACK I know exactly what the RA and DEC tracking rates are because the target drifts no more than 1 or
2 pixels over 4 hours, without the use of an autoguider. So comparing the 200 point model tracking rate with
ATRACK I noticed a consistent error, in both direction and magnitude, which led me to the conclusion there is
some base tracking error in the mount that APCC does not correct for.
Or... the more likely reason, is your scope has unmodeled complex flexure. This can easily cause apparent tracking errors. Changes in temperature of just a few degrees C can change the Young modulus of materials in the scope enough to cause apparent tracking rate changes at the pixel level.

-Ray Gralak
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of PEMPro V3: https://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver


-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Craig Young
Sent: Tuesday, May 5, 2020 2:24 PM
To: main@ap-gto.groups.io
Subject: [ap-gto] Adjust CP4 Clock Frequency

Rolando mentioned in a recent posting (#70144) the tracking rate is dependent on the controller clock frequency.
Over the years of using my AP1600 with encoders I could never get APCC to provide the same tracking accuracy
as other users, even with a 200 point model, so it had to be a problem with this particular mount. Since this has
never be resolved after several hours working with AP I wrote my own tracking program ATRACK which does
provide very accurate tracking over several hours.

With ATRACK I know exactly what the RA and DEC tracking rates are because the target drifts no more than 1 or
2 pixels over 4 hours, without the use of an autoguider. So comparing the 200 point model tracking rate with
ATRACK I noticed a consistent error, in both direction and magnitude, which led me to the conclusion there is
some base tracking error in the mount that APCC does not correct for. One possibility would be the crystal
frequency used for timing. This is a known problem in radios which is why they revert to TCXO devices
(Temperature Compensated Crystal Oscillators). Also, on one of my other mounts, there is a setting to adjust the
master clock frequency. I know the basic tracking of the mount is excellent because ATRACK reports no sudden
jumps (e.g., cable twists or mirror shift, etc). And, if there is a clock frequency error then the encoders will provide
excellent pointing (which they do) but accurate tracking would not work. A 200 sample pointing model can provide
excellent pointing and tracking but the tracking makes an assumption the sidereal tracking rate of the mount is
perfect. If the sidereal rate is too fast, like on my mount, then the model will not know this and accurate tracking is
impossible no matter how big my model sample count or polar alignment.

To test this I ask the guys at Astro-Physics if there is a way to adjust the base clock frequency of the CP4 using
APCC. I made some quick measurements comparing ATRACK rates with APCC rates and found a discrepancy
of 0.1% (0.001). Since APCC is ALWAYS running fast I would then reduce the clock rate by 0.1% and see if it
solves the problem. The adjustment should reduce the tracking rate to match ATRACK.

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

ATrack is used to determine the actual tracking rate.  I know this is correct because the drift (RA,DEC) is +/- 0.57 arcsec or less over 60 seconds, typically about +/- 0.2 arcsec.  If I then turn off ATrack correction and turn on APCC tracking correction (w/refraction) I then get a significant drift.  When comparing the two rates I get: ATrack Rate / APCC rate = approximately 0.001, or 0.1%.  This is consistent no matter which hemisphere or DEC,HA I have the telescope pointed at.  In other words, both ATrack and APCC change the RA and DEC tracking rates to accomodate the error in the mount pointing and refraction.  They both change in the same direction and about the same amount.  The problem I think is the Sidereal Rate is running too fast.  APCC assumes sidereal rate is accurate and adds the pointing model correction to it.  Which means the resultant corrected tracking rate is still running too fast.  So the base Sidereal Rate has to be slowed down by about 0.1%.  On the other hand, if the sidereal rate is corrected using the encoders and the encoder calibration is off then the sidereal rate will be off and APCC tracking correction will also be off.

Craig