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Navigation

Early navigational techniques employed observations of the sun, stars, waves and birdlife. In the 15th century, the Chinese were using the magnetic compass to identify direction of travel. By the 16th century in Europe, navigational instruments included the quadrant, the astrolabe, cross staff, dividers and compass. By the time of the Age of Exploration these tools were being used in combination with a log to measure speed, a lead line to measure soundings, and a lookout to identify potential hazards. Later, an accurate marine sextant became standard for determining latitude and was used with an accurate chronometer to calculate longitude.

Passage planning begins with laying out a route along a chart, which comprises a series of courses between fixes—verifiable locations that confirm the actual track of the ship on the ocean. Once a course has been set, the person at the helm attempts to follow its direction with reference to the compass. The navigator notes the time and speed at each fix to estimate the arrival at the next fix, a process called dead reckoning. For coast-wise navigation, sightings from known landmarks or navigational aids may be used to establish fixes, a process called pilotage. At sea, sailing ships used celestial navigation on a daily schedule, as follows:

Fixes were taken with a marine sextant, which measures the distance of the celestial body above the horizon.