calibration.md

 Here you can find information about calibration from mavlink
 
 https://discuss.bluerobotics.com/t/pixhawk-accelerometer-and-compass-calibration-though-pymavlink/11453/2
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+Accelerometer Calibration
+
+The MAV_CMD_ACCELCAL_VEHICLE_POS 2 command says it’s “Used when doing accelerometer calibration.” That’s a bit ambiguous, but given it’s not working for you then the “when doing” likely implies the calibration has to be started with a different message, and the vehicle pos command is just for stepping through the positions during the calibration.
+
+    From the QGC source file that was linked to in the other post,
+    the APMSensorsComponentController.cc sets up the accelerometer calibration,
+    then delegates it to the vehicle (_vehicle->startCalibration()).
+    Looking in Vehicle.cc (where vehicle functionality is defined),
+    the calibration is started using the MAV_CMD_PREFLIGHT_CALIBRATION 6 command.
+
+Compass Calibration
+
+    For the compass calibration, the definition in APMSensorsComponentController.cc 1 uses MAV_CMD_DO_CANCEL_MAG_CAL 1 to determine whether the flight computer supports onboard compass calibration.
+    Looking at the nearby commands in the message set comes up with the MAV_CMD_DO_START_MAG_CAL 3, which is presumably used to start magnetometer (compass) calibration (so we have something to look for).
+    The calibrateCompass method (from step 1) hands off logic to the _mavCommandResult 4 method in the same file,
+    where you can see that MAV_CMD_DO_START_MAG_CAL 3 is indeed used if onboard calibration is supported,
+    which from a search of MAG_CAL in the ArduPilot codebase 2
+    seems to be the case as of at least ArduSub 4.0 2 (probably can stop here, and just use that message).
+
+    Where onboard calibration isn’t supported, it instead uses _compassCal.startCalibration().
+    I wasn’t sure where that was defined, but it wasn’t in that file so
+    I checked the corresponding header file, which #includes APMCompassCal.h.
+    Looking in the corresponding source file,
+    APMCompassCal.cc 1 defines the function we’re after, as well as the various calculations that are used to perform a compass calibration externally.
+    The code there is quite convoluted, so I’m not certain how it tracks the calibration state (if it even does - it seems like it might just communicate via string/text messages).
+
+    Focusing back on the more promising approach, to confirm whether the MAG_CAL messages work I tried following the QGC approach from step 3. - sending a CANCEL_MAG_CAL command and seeing what kind of MAV_RESULT 1 the command is acknowledged with (as per the Command Protocol 1):
+