Dead reckoning (DR) is a method of navigation in which a ship (and later, aircraft) seeks to determine its bearings. Starting from a known position, the pilot tracks the course and speed of his vessel over a precise period, making some adjustment for drift. Celestial navigation devices are not employed, except to make corrections ("fixes").
Dead reckoning has always been plagued by inaccuracy, especially when used over long periods and distances. Such factors as ocean currents, wind and the difficulty of accurately gauging speed, contribute to error.
In general, modern-day, inexpensive global positioning satellite (GPS) devices and other electronic gear have made dead reckoning the preserve of maritime historians and hobbyists.