Accelerometers measure linear acceleration as long as there is no rotation. When an accelerometer is rotated, the force of gravity is measured as well and there is no way to distinguish between the two different contributions. MEMS gyroscopes generate an output signal directly proportional to the angular rate by measuring the force generated by the Coriolis effect. By using a gyroscope, angular rotations are measured while linear displacements are not. Accelerometers and Gyroscopes can be combined to create an Inertial Measurement Unit or IMU.