Dead Reckoning

For many years, the practice of keeping a log based on estimated speed was called ‘deduced’ reckoning. Over time, this turned into dead reckoning. Dead reckoning is the process by which the position of the ship at any moment is found (without any observation of the sun or stars) based upon the last well-determined position and the run that has been made since that last position.  For this purpose, the ship’s course indicated by its compass, the distance indicated by the log, and drift and leeway were all taken into account. A nautical term that has now become part of everyday language