Before the invention of GPS, before LORAN (a navigation system used before GPS), and even before airplanes had radios at all, if you wanted to fly long distances you might use sightings of the sun in the daytime or the stars at night. But if it was cloudy, you’d need a different system. You’d use an estimate of your airspeed and direction, and factor in as much as you knew about the speed and direction of the wind outside your plane. It was pretty much just an educated guess, but it worked reasonably well. Most of the time.
That method of navigation is called “dead reckoning”. And that’s a term that doesn’t really make sense; there’s really nothing dead about it (unless of course you’re really bad at it). That’s why in 1931 in a manual about airplane navigation called Avigation, Bradley Jones explained that it wasn’t “dead” reckoning, it was “ded” reckoning, and “ded” stood for “deduced.” This made more sense to practical-minded aviators, and it became generally accepted, at least among those who even noticed that there was such a thing as airplane navigation.
There is a bit of a problem, though, represented by this: “Keeping a true, not a dead reckoning of his course.” That was written by Mark Ridley in “A short treatise of magnetic bodies and motions.” And he wrote it in 1613. Dead reckoning, you see, was a navigation method for ships centuries before its use in airplanes. And not once in those hundreds of years did anybody refer to it as “deduced reckoning” or “ded reckoning.”
Of course, there’s also a problem with the problem. Although there’s a glaring lack of corroboration for the “deduced reckoning” theory, looking at the historical record doesn’t suggest any alternative ideas about where “dead reckoning” might have come from. There’s an old use of “dead” that means “absolute,” which might be it. Or it might have something to do with “dead ahead.” or maybe it really did refer to the disastrous results you might get if you navigated by guesswork for too long, but really nobody knows. There’s just not enough information to deduce an answer, I reckon.
