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a colorimeter designed for measuring the color of the clear daytime sky. A cyanometer has a one-dimensional scale that makes it possible to measure colors in the sequence from white through whitish blue to saturated blue. A distinction is made between relative and absolute cyanometers. With relative cyanometers, the color of the sky is compared with a set of standards; for example, the cyanometer devised by Saussure uses slips of paper tinted various shades of blue as the standards. Absolute cyanometers make it possible to express observational results as a color temperature or some other color characteristic used in colorimetry. The first cyanometer was fabricated by H. B. Saussure in the late 18th century. In 1919, G. A. Tikhov invented a cyanometer in which the color of the sky is compared with the color of a sapphire plate.