The Inertial Sensor is a combination of a 3-axis (X,Y, and Z) accelerometer and a 3-axis gyroscope. The accelerometer measures linear acceleration of the robot (including gravity), while the gyroscope electronically measures the rate of rotation about the V5 inertial sensor three-axis.
The combination of these two devices in one sensor allows for effective and accurate navigation, as well as controlling any change in the motion of a robot.