The latest Slam Stick release has an IMU capable of recording the device's orientation relative to either its initial orientation (relative orientation), or to relative to magnetic north (absolute orientation). As I discuss elsewhere, the sensor uses a magnetometer to measure the Earth's magnetic field for absolute orientation, along with the accelerometer and gyroscope used to track gravity and the device's movement. The algorithms to synthesize these sensors into one set of coordinates are relatively complicated, and they need to go through a calibration procedure to become accurate.