It's this way... Or was it that way?
Inertial Measurement Units (IMU's) are components that determine location or distance based on recording and calculating movement. IMU's can be used as a standalone system, or integrated into another to increase accuracy, especially when combined with a GPS.
An IMU can determine distance and movement in a variety of ways, such as using accelerometers, gyroscopes, or magnetometers. Each component works complimentary to each other to bring movement positioning to precision accuracy.