When it is the beginning , the navigator is clearly aware of the position/location. When he starts to move (in the mid-sea or mid sky), he can get some known (measured) factors other than the position/location in terms of a fixed landmark . They are, The direction of movement (by using a compass) Speed of movement Time taken to reach each heading Using all this information, the navigator calculates the distance and route which he has covered and keeps track of his movement by plotting a nautical chart ( also called a sea chart). This technique is known as Dead reckoning . In brief, Dead recko ning is a process to determine the position of the navigator (sailing a ship or flying an aircraft) using the record of courses that have been sailed (or flown), the distance covered (by using the velocity in which he has traveled and time taken to reach the next course from the previous course), known point (the previous point is the known point) and the estimated or known or approximated ...