Dead reckoning

Q From Don Monson: I just came across this sentence about navigation from an old Flight Simulator book: “Dead reckoning (DR), sometimes referred to as ‘ded reckoning’ since it is short for ‘deduced reckoning,’ is actually a more scientific approach to navigation than pilotage.” Is this origin for the term correct?

A It’s always fun to learn about a popular etymology. No, it’s not correct. Not even close.

But a search shows that the story is widely believed and appears in a lot of reference books, mainly US ones on navigation. I’ve even found an example in a US patent (number 6046565): “Ded-reckoning, often called dead-reckoning in error, is a shortening of the term deduced reckoning.”

I’m indebted to The Straight Dope for a detailed discussion of the matter back in 2002, which is much fuller than I would attempt here. In essence, the writer states that the tale is first recorded in a work of 1931 but that it became common during World War Two. My own enquiries support the latter point, examples starting with Leland Lovette’s 1939 book, Naval Customs, Traditions and Usage, and becoming frequent during the war years. It seems to have got a fair hold on people by the time this item appeared in the Oakland Tribune on 24 January 1947:

A friend of mine who prides himself on being a precisionist, went to see “Dead Reckoning” the other night and I asked him how he liked it. “Oh, the picture was fine,” he said, “but the title ...” “What’s wrong with the title?” I asked. He looked down his nose at me. “There’s no such thing as ‘dead reckoning’,” he replied. “It’s ‘Ded’ Reckoning, which is short for ‘Deduced Reckoning’. Ask any navigator.”

This supposed derivation is given some credence in the Fourth Edition of the American Heritage Dictionary, which states the story without any alternative, though it does prefix it with “possibly”. Every other dictionary on my shelves either keeps quiet or follows the evidence that’s laid out in the Oxford English Dictionary.

That shows that dead reckoning, in that spelling, has been in the language since the early seventeenth century. It had much the same sense then as it does now, that of estimating the position of a vessel from its speed, direction of travel and time elapsed, making use of log, compass and clock. The alternatives were pilotage, which made use of visible landmarks, and celestial navigation by the sun, moon and stars.

What makes deduced reckoning and ded reckoning seem plausible is that dead reckoning doesn’t make sense, even though you might end up dead if you got your sums wrong. Writers are divided on which sense of dead the old-time mariners had in mind. Was it perhaps the idea of being as still as a corpse, so referring your position to a point that’s dead in the water? Or is it something completely or absolutely so, exact or precise, as in dead level, dead wrong, or dead ahead? The OED plumps for the latter.

As so often happens, we are left in a state of less-than-perfect understanding about the reason for an expression coming into being, but the one thing we can be sure of is that dead reckoning has no link with deduced reckoning or the abbreviated ded. reckoning.