There are several commands to calibrate the various sensors on the APM:
Initiates the accelerometer calibration routines. This is the “place the UAV on its left side…” routine.
Does a simple pre-flight accelerometer calibration
Initiates the gyro calibration routines.
Initiates the pressure sensor calibration routines.
Initiates the magnetometer/motor interference calibration routines.
Do a levelling routine on a multicopter.
Perform calibration of the RC input channels.
Performs a full ground start. This includes gyro and pressure sensor calibration. It is automatically performed when the autopilot receives an arming command.
Magnetometer (compass) calibration to account for any soft-iron sources on the UAV.
Do a AHRS trim.