GPS and other navigation systems are well worth the time to look into. something like Decca or LORAN are really simple to understand: two or more base stations

GPS and other navigation systems are well worth the time to look into. something like Decca or LORAN are really simple to understand: two or more base stations in a known location emitting phase locked signals. By counting the nodes/antinodes of the harmonics, you can work out how far away you are from the base stations. The downside is that you need a initial fix to work out absolute location. The thing thats kinda touched on here is that GPS uses clocks to allow the receiver to work out how long the signal has been in flight (simplification) If you know where the satellites are (using the Almanac of satellite positions) you can get your location by fairly simple triangulation. Now, you don't have an atomic clock on your receiver, so how can you accurately measure the time difference between signals? for GPS you only need to know the relative time difference between each satellite, and even thought quartz clocks are only accurate to seconds a year, in the ~20-50ms it takes for the signal to arrive, its more than accurate enough. However that means you are open to spoofing, because you sync your local clock to a satellite, you have no real way of detecting if the clock has skipped. If you have an accurate clock source, you can then validate the clocks that are on the transmitters. I think, but can't confidently assert that calculating position becomes easier because you have an authoritative clock source, so don't need to piss about with clock sync using an unknown time offset. I think the implication is that this provides a strong form of signal authentication. However chipscale super-stable clock references also allow more autonomous styles of navigation. (ie celestial)