"Dead Reckoning is the process of estimating your position by advancing a known position using course, speed, time and distance to be traveled. In other words figuring out where you will be at a certain time if you hold the speed, time and course you plan to travel."

Further... "The Chinese discovered that a needle with a magnet on one end always pointed the same direction, north. At least now they could know what direction they were headed in, and if you knew that and you multiplied your speed by your time spent traveling you could deduce your position. This is called 'Dead Reckoning' and was used regularly well into this century. However it wasn't terribly accurate since it relied too much on estimates of speed."

Even more... "According to popular definition, dead reckoning is short for "deduced reckoning" or, as the old-timers used to say "you're dead if you don't reckon right." In truth, however, the term originated with maritime navigation and refers to "reckoning or reasoning (one's position) relative to something stationary or dead in the water." Simply stated, DR navigation is a method of precluding en route progress based on the direction of travel and the estimated speed since the last known position."