Originally Posted by
Maninthebar
That source of all error, Wikipedia, says "The term "dead reckoning" was not originally used to abbreviate "deduced reckoning," nor is it a misspelling of the term "ded reckoning." The use of "ded" or "deduced reckoning" appeared much later in history, no earlier than 1931; in contrast to "dead reckoning" appearing as early as 1613 in the Oxford English Dictionary. The original intention of "dead" in the term is not clear however. Whether it is used to convey "absolute" as in "dead ahead," reckoning using other objects that are "dead in the water," or using reckoning properly "you’re dead if you don’t reckon right," is not known"
One might also instantiate "dead on", "dead heat", "dead drunk" in each of which the term 'dead' qualifies as 'absolutely'
That said if I was responsible for navigation the most common meaning of dead would most likely also apply.