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