Ring Dial (brass, necklace)

In the 15th century, sailors estimated their latitude by the height of the stars in the sky. Looking for greater precision in the measurement of the height of the Sun, Pedro Nunes 1573 invented an instrument that became known as the nautical ring dial. It's a ring whose centre is movable. When held vertically, a little hole lets the sun shine through onto the hours written on the inside. It has a corrective device in the holding throne (hanger) and can be used for a series of parallel latitudes 20 30 40 50 60.