To help anyone looking into the data from the motion box/IMU (Inertial Measurement Unit) it's probably really cool to give a brief explanation on the sensors in there.
The motion box contains a I2C bus that connects the arduino to three different sensors:
All the values are captured digitally through the I2C bus from this sensors (except for pre-US OPEN data when the ADXL335 was used; in those cases the reading was made using arduino's ADC).
The orientation of this sensors on the board vary a little bit depending on how the motion box is mounted on the board; that sometimes changes depending on the rider's stance.
Better than a thousand words: