This looks like pretty good guiding to me but I never really understood how to read the vertical lines in the chart. I understand it shows the corrections but how should it be interpreted ? Is it correcting too much, not enough ? Should I change the settings or be happy with sub 0.50” total error with an EQM-35 Pro mount and touch nothing ?
📷 IMG_0255.png
📷 IMG_0256.png
You should be happy with 0.5” RMS…
If your stars are round, don't touch it.
Yeah I think guiding is one of those things, like flats, that don’t need to be looked at unless it’s not working. It’s easy to get hung up on the minutae of it but if your images are good then don’t worry about it.
Is that the Touch n Stars app? Are you on a tablet there?
It’s a Touptek StellaVita on a iPad mini 5
Eric Gagne · Apr 8, 2026, 02:07 AM
This looks like pretty good guiding to me but I never really understood how to read the vertical lines in the chart. I understand it shows the corrections but how should it be interpreted ? Is it correcting too much, not enough ? Should I change the settings or be happy with sub 0.50” total error with an EQM-35 Pro mount and touch nothing ?
📷 IMG_0255.png
The EQM-35 can be a rough mount at times. I think you’re doing pretty well here though.
To understand a little more about the graph and what you’re seeing:
The size of the ‘corrections’ which are the vertical bars you see are irrelevant and PHD scales these bars so that you can see them. What you want to see however, is if PHD applies a correction, the horizontal line returns to center within 1 or 2 total corrections. If it takes more than this, you should increase your guide rate, or aggressiveness. On the flip side, if you see the mount over correcting, creating a zig zag or sawtooth action, you should turn down your rates, aggressiveness, or investigate your MnMo.
MnMo or ‘Minimum Move’ is a value that will be different for every setup. This value is measured in pixels, however you should consider a realistic expectation for the performance of your mount. If you only expect 0.5 arc second RMS performance from something like an EQM-35, then your Minimum Move should be equal to 0.5 arc second. Calculate your pixel scale/sampling of your guide camera accordingly and convert 0.5 arc second into a pixel value. I cannot interpolate your image scale from these screenshots unfortunately, but based on the graph I think your settings are fine.
Lastly, things that people really tend to overlook often is seeing conditions. I often see people complain that their mount works great one night, and the following night they have extremely poor performance, often tweaking their settings to try and get the mount to perform better. These folks get frustrated, blame the mount, and in worst cases I suspect they’re probably returning products because of it. This is all because of seeing!!! Once you have your mount dialed in on a good night, don’t touch the settings, just leave them be as you simply cannot overcome something that’s out of your control.
The easiest way to identify bad seeing conditions is to watch the guide graph motion. If you see saw tooth action on both the RA and the DEC axis, this is almost always bad seeing. This is that twinkle in the stars, the high frequency motion, the ripples in the atmosphere. If you see the saw tooth motion on a single axis and not the other, then you have something wrong with either your settings or your mount. Often times, the declination axis is the main indicator of seeing, this is because declination in a perfect system should not have to move much, if at all.
The PHD2 help guide is really intuitive, I highly encourage you to read it. There are tons of great points that I wont be able to hit on here. If you have any further questions though, I will try to answer them.
Thanks for the explanation Brian. The seeing was not very good last night, below average. My resolution is 1.22”/pixel so I am not worried about anything as long as my total error stays under 1“.
I was curious as to how to read this graph.