Measurement history

Scholars and navigators are well aware that if the position of celestial bodies can be accurately measured on the sea surface, then sailors can know their latitude with relative certainty. To do this, sophisticated measuring instruments are required.
Ptolemy once depicted the astrolabe (also known as the astrolabe). Larger astrolabes are used in observatories and smaller ones in ships. Using the astrolabe required the cooperation of three people—one grasped the thumb ring on the astrolabe, one aimed, and the third read the results on the dial. When the ship shakes more violently, the results obtained are naturally not very accurate. Whenever possible, seafarers went ashore to take measurements.
Ancient astronomers used the cross to measure the latitude of the stars, and later sailors also used it in navigation. This instrument consists of a ruler and a cross-shaped ruler, the lower end of which is placed in a horizontal position. While looking at the celestial object along the scale, slide the cross-shaped ruler until it touches the object (sun or star) in your field of view, then read off the degree on the scale. This instrument can be operated by only one person.
Both the astrolabe and crosshair require the observer to look directly at the sun. On sunny days, too much light will make observations impossible. To solve this problem, English captain and navigator John Davies invented the dorsal scale. It consists of a ruler and a crossbar that slides. The observer looks away from the sun and slides the bar until it casts a shadow on the small plate in front of it. In this way, the observer can observe the horizon.
John Davies also invented the quadrant with the help of Edward Wright, a mathematician from Cambridge. On the crosspiece of this instrument was an eyepiece through which the observer could observe the horizon and the reflected sun.
Kreutschke's hydrogeographer, Pierre Bougol, made further improvements to the quadrant, which enabled the observer through the eyepiece to see the sun set on the horizon.
The octant was invented by John Hadley in England and first tried in 1732. It consists of a reflecting telescope and a spirit level. This instrument was more accurate than any other instrument ever used at sea.