Z accel = Data1 And 0x7F + Data2 / 0x100
If (Data1 And 0x80)=1 Then Z_Accel = -Z_Accel
Vertical (Z) acceleration is positive for accelerating upwards (e.g. driving through a dip), negative for accelerating downwards (e.g. driving over a brow). This results in a stationary and level vertical acceleration of +1g (due to gravity).