I quickly checked the code, and it seems to me that binning is correctly accounted for when computing the internal guider's rms error.
Read on if you're interested to see the details in the code:
Here's where the "drift" (difference is RA or DEC in arc-seconds) for a given time sample is computed:
invent.kde.org/education/kstars/-/blob/m...uide/gmath.cpp#L1130
Those "arc" variables (meaning they are in units of arc-seconds as opposed to pixels) are computed slightly above:
invent.kde.org/education/kstars/-/blob/m...uide/gmath.cpp#L1122
The "convertToArcseconds() method can be found here:
invent.kde.org/education/kstars/-/blob/m.../calibration.cpp#L65
wherexArcsecondsPerPixel() and yArcsecondsPerPixel() seem to take binning into account:
invent.kde.org/education/kstars/-/blob/m...calibration.cpp#L107
If you wanted to double check that these calculations were being done properly,
you could look at the guiding log being stored at a sister directory to the logs directory
(e.g. on linux that's ~/.local/share/kstars/guidelogs) and look at the header of your most recent guide log,
e.g. mine from last night looks like this:
KStars version 3.5.5. PHD2 log version 2.5. Log enabled at 2021-08-04 22:42:34
Guiding Begins at 2021-08-04 22:42:34
Pixel scale = 3.87 arc-sec/px, Binning = 2, Focal length = 400 mm
RA = 22.64 hr, Dec = 34.5 deg, Hour angle = N/A hr, Pier side = West, Rotator pos = N/A, Alt = 40.6 deg, Az = 73.5 deg
Mount = mount, xAngle = 128.5, xRate = 1.599, yAngle = 219.4, yRate = 1.788
Frame,Time,mount,dx,dy,RARawDistance,DECRawDistance,RAGuideDistance,DECGuideDistance,RADuration,RADirection,DECDuration,DECDirection,XStep,YStep,StarMass,SNR,ErrorCode
1,3.488,"Mount",0.000,0.000,0.021,-0.045,0.000,0.000,0,W,0,,,,3045,39.02,0
2,6.798,"Mount",0.058,-0.047,0.027,-0.036,0.000,0.000,0,W,0,,,,3039,38.98,0
3,10.246,"Mount",-0.042,0.018,-0.063,-0.059,-0.037,-0.054,23,E,30,N,,,3108,39.42,0
Yours may be a bit different, as I store the calibration, and thus there is no calibration at the start.
Search for the line that looks like
Pixel scale = 3.87 arc-sec/px, Binning = 2, Focal length = 400 mm
and you can see whether the parameters look right.
E.g. that line is printed by
invent.kde.org/education/kstars/-/blob/m...de/guidelog.cpp#L152
where info.pixelScale is filled in here:
invent.kde.org/education/kstars/-/blob/m...rnalguider.cpp#L1608