FYI, here is a part which is still relevant today: "the system continuously ironed out accumulated errors over time by comparing actual distances driven and turns made with road shapes on the map. Honey calls the technique "augmented dead reckoning." That means driving through a long stretch of straight highway could begin to trip up Etak's system, since there were no turns and no distinct roads for the computer to a…
Airliners used the same basic system for a long time... and it was, in fact, an airline incident that lead the US gov't to declassify GPS so trans-oceanic flights could be tracked better. To this day though, when I pilot starts up an airliner, they fire up that old system as a backup, its programed down to the gates at the airports, so they set their departure gate and as soon as they start moving, it tracks, through…
"According to the ICAO, the autopilot was not operating in the INS mode either because the crew did not switch the autopilot to the INS mode (shortly after Cairn Mountain), or they did select the INS mode, but the computer did not transition from INERTIAL NAVIGATION ARMED to INS mode because the aircraft had already deviated off track by more than the 7.5 nautical miles (13.9 km) tolerance permitted by the inertial navigation computer. Whatever the reason, the autopilot remained in the HEADING mode, and the problem was not detected by the crew."