Dead reckoning is a technique to determine a ship’s approximate position by applying to the last established charted position a vector or series of vectors representing true courses and speed. This means that if we have an earlier fix, we plot from that position our course and “distance travelled since then” and deduce our current position.
Dead reckoning is the process of determining one’s present position by projecting course(s) and speed(s) from a known past position, and predicting a future position by projecting course(s) and speed(s) from a known present position
In the other words dead reckoning can be explained as :
Dead reckoning, determination without the aid of celestial navigation of the position of a ship from the record of the courses sailed or flown, the distance made (which can be estimated from velocity), the known starting point, and the known or estimated drift.
Some marine navigators differentiate between the dead-reckoning position, for which they use the course steered and their estimated speed through the water, and the estimated position, which is the dead-reckoning position corrected for effects of current, wind, and other factors.