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orthographic planisphere: flat map produced by orthographic projection.
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pedometer: device worn by a walker to measure distance by counting paces.
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pendant sundial: a form of sundial suspended by a cord and possibly hung around the neck.
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perpetual calendar: calendar covering a number of years, see article on time and date.
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phase of the moon: the changing appearance of the moon throughout its approximately monthly cycle, from the thin crescent of new moon to the complete circle of full moon and back again.
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pillar dial: type of altitude dial, see article on the sundial.
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pin gnomon: the part of a sundial which casts the shadow, where this part is in the form of a pin.
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plane table: type of surveying instrument, see article on the plane table.
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plane table alidade: an alidade specially adapted for use with a plane table.
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planetary hours: system of hour reckoning, see article on time and date.
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planetary temperaments: astrological character of the fixed stars; as assigned in classical astrology, each star had a nature and effect similar to one or more of the planets.
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planisphere: a representation of a spherical body on a flat surface, commonly a map of the earth or of the heavens.
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planispheric astrolabe: astronomical instrument based on a planispheric projection of the heavens, see article on the astrolabe.
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plate: part of an astrolabe with a projection of altitude and azimuth lines on to the equatorial plane, see article on the astrolabe.
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plumb level: device for determining a horizontal level or an angle of elevation by a plumb line or plummet.
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plumb line: a suspended thread with a weight at its end, indicating the vertical.
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plummet: a form of plumb line in which the 'line' and weight are a single rigid piece.
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polar dial: type of sundial, see article on the sundial.
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polyhedral dial: sundial with hour lines on various faces of a solid figure, see article on the sundial.
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prime vertical: celestial great circle passing through the east and west points and the zenith.
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