That's pretty neat. Any idea on how accurate it was? The real breakthrough in navigation imo is not so much the display of a map but rather the lack of display of more data than you actually need at the moment. Turn-by-turn navigation is what then really drove adoption. GPS may not have been necessary to achieve this and this article is a nice reminder that there are more ways than one to skin a cat.

Do any present day navigators use inertial guidance when they are out of reach of satellites? (I know mine doesn't when I enter a tunnel it seems to continue to coast based on the last known info when the signal was lost, after more than a few minutes, for instance a traffic jam it gets wildly erratic.)