The X, Y, and Z values are from the three magnetometers of the compass; one each on the X, Y, and Z axis. A magnetometer will be at maximum when it's pointed into (or parallel) to the geomagnetic flux. That's why Y is 0 when the A/C is pointed north; it's perpendicular to the geomagnetic flux.I hope you are able to figure this out from the .dat file. I have been testing the compass and wanted to know what the x, y and z where about. I've read here that mod should be around 1400.
So far, and I have more testing to do, I found that the compass reports the axis to the processor
and that when the aircraft is level the y ( value in sensors of the Go app) is zero(or close) when pointed north or south .
So pointed north , y=o, x= + 400 to 500, z=around 1300, mod around 1400
south y=0, x= -400 to -500, z and mod are same
east y= -400 to -500, x=0, z and mod are same
west y=+400 to 500, x=0, z and mod are same
Now what has been suggested might be a clue as when the aircraft is pitched the numbers all change in a strange way.
I wondered why we needed to point the nose down during calibration and it seems to record in the z axis.
I wonder if the pointing down angle is a bit more critical than it seems?
Is it possible if when doing the calibration we hold it down ,not at exactly a straight down angle but slightly off we record an error in the calibration data that doesn't show up except in specific pitch conditions?
It's unflyable with the weather we have next few days but I'll test as soon as I can.
The following is an excerpt of a post I did recently. Maybe it addresses your question.
Contrary to popular belief the compass calibration is not about discovering which way is North. Rather, it's purpose is to adjust the gain of each of the X, Y, and Z magnetometers so that they have a uniform response to the geomagnetic field. All that's really required is that the P3 be oriented in enough different directions so that each magnetometer is exposed to a range of values.The first step of the compass dance gathers that data for the X, and Y magnetometers. The second step has the Z axis pointing at the horizon so that the data can be gathered for it.It probably doesn't matter that it's the X axis pointing at the horizon instead of the Y axis. I.e., right side down should work just as well as nose down for the 2nd step.
I once did an experiment where the compass dance was done upside down. 1st step top down, and 2nd step nose up instead of down. I had carefully measured the X, Y, Z, MOD numbers before and and after and didn't see any difference. Flew fine.