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Butterfield dial: type of sundial adjustable for latitude, whose gnomon incorporates a latitude pointer often in the form of a bird. This dial type is associated with the 17th-century Paris-based English maker Michael Butterfield.
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calendar: system of reckoning dates, see article on time and date.
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calendar-zodiac scale: scales relating the sun's position in the zodiac to the date.
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caliper: instrument used to take dimensions. One type has two curved legs whose endpoints are used to determine the diameters of spheres.
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Cardan suspension: universal mounting attributed to the 16th-century Italian philosopher and physician Girolamo Cardano which, by means of gimbals, allows the supported part to remain horizontal irrespective of the orientation of the rest of the instrument.
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cardinal points: the main directions on the mariner's compass, north, south, east and west.
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carpenter's rule: measuring ruler carrying one or more scales for calculating the volume of timber or the surface area of board or planking.
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celestial globe: globe marked with the positions of the stars.
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celestial planisphere: map of the heavens, produced by geometrical projection of a sphere on to a flat surface. A common example of the use of a form of planisphere is the rete of an astrolabe.
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celestial poles: diametrically opposite points of the celestial sphere about which the heavens are observed to rotate once a day.
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