NavList:

Paul Dolkas, you wrote:
"…so where does "Dead Reckoning" come from? (I kinda liked the "deduced" theory myself.)"

Clearly it's a satisfying story, which is why it has spread. This is a common feature of "folk etymologies".

No one knows for sure where the phrase "dead reckoning" originated, but it's been around for centuries. In the nautical world, "dead" traditionally meant motionless as in "dead in the water". This is probably the sense of it in "dead reckoning" since the calculation assumes that the water through which the vessel is travelling is "dead" or lacking in currents. Though we know that there are always currents to a greater or lesser degree, we work the calculations as if the water is dead. By the way, a reckoning is just an older word for a calculation, so a "deduced reckoning" would seem to be somewhat redundant in any case.

Popular turns of phrase and coined words achieve their popularity through a complicated process. It's not top-down. It's a function of fashion and even the amusement of word play. I suspect that the jokes people have made about "dead reckoning" over the years have helped to keep in the navigator's dictionary.

The theory that dead reckoning was short for "deduced reckoning" was apparently first published as a letter to the editor of a London newspaper in the 1920s (I don't have the specifics right in front of me). The author of that letter created an air of scholarship around his theory by talking about his research in old 17th century logbooks where he says that it was spelled "ded" and shortened in order to fit into the columns available. Alternate spellings were normal in that period so that tells us nothing. And his evidence evaporates when you dig through those period logbooks. There's certainly no smoking gun. The "deduced reckoning" story spread quickly and it was especially popular among aviators. Long-distance air navigation was developing very rapidly at that time, and since aviators would not have been familiar with a nautical term like "dead reckoning", it appears that community was eager to adopt this explanation. Likewise this folk etymology has become popular in robotics in recent years probably for the same reason.

-FER

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