Using the NXT Brick (sold separately), the Compass Sensor is able to measure the earth's magnetic field and calculates a magnetic heading to tell which direction your robot is facing. The compass has a built-in calibration to help reduce magnetic interference from other sources. Includes 1 Compass Sensor. Does not include connector cable. This is the individual component, and does not include the NXT Intelligent Brick, software or any accessories. It requires the complete LEGO® MINDSTORMS® NXT set (#8527 or #8547) for use.