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octant: the eighth part of a circle or an instrument measuring up to 45 degrees.
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old quadrant: type of horary quadrant, see article on the quadrant.
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opposition: two planets 180? from each other in the ecliptic are said to be in opposition. This relative position had important astrological significance.
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ordinary hours: system of hour reckoning, see article on time and date.
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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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