The inertial guidance system was a technological component of a starship that measured the distance traveled and automatically adjusted the course of a ship. When the system malfunctioned, the course adjustments were done manually.
Aboard Galaxy-class starships, information from this component could be downloaded to and accessed from the operations station on the bridge. This information could be later confirmed on the Conn console.
In early 2365, while the USS Enterprise-D was attempting to leave the void in the Morgana Quadrant for the Cornelian system, Lieutenant Commander Data reported that the inertial guidance system showed that seven parsecs had been traveled. Acting Ensign Wesley Crusher confirmed what Data had reported. (TNG: "Where Silence Has Lease")