"This procedure can be likened to a hike with no navigational aids along a narrow, tortuous trail through a forest obscured by fog so impenetrable that one can see only one step ahead. As long as one remains on and follows the trail exactly, there is no ambiguity concerning the proper direction to walk in. As soon as one leaves the main trail, however, then returning to the original trail would be impossible barring incredible luck. One way to leave the main trail "reversibly," that is, so that one can find one's way back to it, would be to carry some marker, say, a length of string, one end of which would be staked to the main trail and which would be unwound as one walked into the forest. One would then simply follow the string back in order to return to the main trail. "
This paragraph comes from the patent (link above). Obviously, I am being slightly facetious and the patent itself provides all the gory details.
Comments