etymology of the term
"There is disagreement about the derivation of the phrase. It is popularly thought to come from deduced reckoning and is sometimes given in modern sources as an alternatively spelled ded reckoning; however, according to the Oxford English Dictionary, the phrase dead reckoning dates from Elizabethan times (1605-1615).The popular etymology from deduced is not documented in the Oxford English Dictionary or any other historical dictionary. Dead reckoning is navigation without stellar observation. With stellar observation, you are "live," working with the stars and the movement of the planet. With logs, compasses, clocks, but no sky, you are working "dead."