Charts, accurate timepieces, and instruments for calculating the noontime angle of the sun were needed to safely navigate the globe.
Before modern electronic navigation tools such as GPS, there were two types of navigation. The first was dead reckoning, in which a vessel’s position was estimated by observing local winds, currents, vessel speed, and direction. This worked best for coastal shipping, where sight of land could help determine location.
The more accurate celestial navigation used the positions of certain stars to calculate a ship’s precise position, using charts and an instrument to measure sun angles over the horizon. An accurate timepiece to determine exact noontime for sights also was needed, along with elaborate mathematical tables to calculate the precise position on the globe.