dead reckoning

• ded reckoning

Uncertain. Not short for deduced or deductive, but this belief explains the alternative spelling ded reckoning (which actually originated centuries later).

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dead reckoning (countable and uncountable, plural dead reckonings)

1. A method of estimating the position of a ship or aircraft by applying estimates of the distance and direction travelled from a previously known position. In respect to ships/boats, it excludes the effect of wind and current on the vessel. Compare with estimated position. Abbreviation: DR