With the advancement of atomic clocks and the ability to make them hand held (it can be done, just not at a commerically viable level yet)
1979...Staff Sergeant Kukri in a swamp near MacDill Air Force base in central Florida, lugs a 75-pound pack of electronic gear, with a 12-foot whip antenna, sweating his (then) skinny arse off, and strains to hear the reassuring "beep-beep" in his headphones of the confirmation signal from the invisible satellite above - telling him that he is indeed in grid square UT26898882 - which he knows to be true by visual observation, and old-fashioned land-nav techniques...and he ponders, between swipes of his face with his trusty hanky, what it means to have a eye-in-the-sky tell one where one is.

And it amazes SSG Kukri that such devices get carried in one's shirt-pocket these days.