An Inertial Measurement Unit is an important part of any starship. It is about the size of a small coin, and it detects changes in inertia so that a starship can pilot itself automatically and not kill all the organic tissue inside because of excess acceleration. It also allows precise movement to be made.
It measures inertia by having patterns of light reflected back on themselves inside the unit and watching the phase change in the light as the IMU is moved from one location to another (i.e. its inertial changes). It uses the theoretical equation $ P = mv $ to perform its calculations. This device is an improvement on ring-laser-gyros (RLG).
Because of its size and inexpensive nature, it is used by every spacefaring species including the Nietzcheans, Systems Commonwealth ships like the Andromeda Ascendant, and pirates and other commercial craft like the Eureka Maru.