Wired yesterday had a cool brief history of GPS.   I learned a couple of cool things:

The GPS story starts with Sputnik, the first artificial satellite. The night after it was launched by the Soviet Union in 1957, researchers at MIT were able to track Sputnik’s orbit by its radio signal. And if you can track satellites from Earth, you can figure out how to locate objects on (or just above) Earth from the positions of satellites. […]

[Today,] GPS augmentation and precise monitoring techniques known as carrier-phase enhancement, differential GPS and relative kinematic positioning can now provide accuracy down to 4 inches.

4 inches! Incredible!   Hmm, if I were 4 inches to the right of where I’m sitting now, I’d fall off the couch.

(Photo: Wired article via NASA)