In article , Marc J. Zeitlin wrote:
To send us off on another tangent, and one that I haven't seen mentioned
in this thread before, it's "ded-reckoning", not "dead-reckoning". The
"ded" stands for "deduced", not whatever "dead" might stand for other
than the obvious.

Dead does not stand for anything.
From http://www.absoluteastronomy.com/enc..._reckoning.htm :

There is some controversy about the derivation of the phrase. It is
popularly thought to come from deduced reckoning and is sometimes given
in modern sources as 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".
--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"