The DeviceMotionEvent.rotationRate read-only property returns the rate at which the device is rotating around each of its axes in degrees per second.
Note: If the hardware isn't capable of providing this information, this property returns null.
The rotationRate property is a read only object describing the rotation rates of the device around each of its axes:
alpha -
The rate at which the device is rotating about its Z axis; that is, being twisted about a line perpendicular to the screen.
beta -
The rate at which the device is rotating about its X axis; that is, front to back.
gamma -
The rate at which the device is rotating about its Y axis; that is, side to side.