The term ‘dead reckoning’, so the Admiralty Navigation Manual (1938) says, is a corruption of the old ‘ded-uced reckoning’ or ‘position by account’, and is used to cover all positions that are obtained from ‘the course the ship steers and her speed through the water, and from no other factors.’ (The last italics are ours.) Had Master William Borough, Chief Pilot of the Muscovy Company, and presently to be appointed to Queen Elizabeth's Navy Board, come across this definition, he would have picked a two-fold quarrel with their present Lordships at Whitehall. For his use and explanation of the term is the earliest of which we have knowledge, although it does not appear even then to have been new.