出典:Wikipedia
出典:『Wikipedia』 (2010/04/14 06:12 UTC 版)
The shadow square, also known as an altitude scale, was an instrument used to determine the linear height of an object, in conjunction with the alidade, for angular observations. It is an early example of an analog computer. It was invented by Muhammad ibn Mūsā al-Khwārizmī in 9th-century Baghdad. Shadow squares are often found on the backs of astrolabes.