Well thats right, in an automobile, if the accelerometer is fixed in a horizontal position, then you
would look at the x and y and ignore the z.
The problem with this approach though, it is when the car is flying through the air or rolling over,
you won't actually get a good reading for the acceleration from the x and y then.
The real problem here, is that all the actual calculations are buried those calls to functions of "accelero",
and we have no idea what they are. That code doesn't looks remotely like my implementations for that device.