การคำนวณตำแหน่งโดยไม่มีอ้างอิงภายนอก

Before GPS, dead reckoning was the primary open-ocean navigation method. Errors accumulate over time because small inaccuracies in speed or direction compound with each calculation. Columbus used dead reckoning to cross the Atlantic, and Apollo mission computers used it to track the spacecraft's position between Earth and the Moon. Modern inertial navigation systems automate the same principle with accelerometers and gyroscopes.