chalice dial: sundial where the hour lines are inscribed on the inside surface of a goblet. A second set of lines can be included to allow for refraction, when the goblet is full. See also scaphe dial.
circumferentor: form of surveying compass with fixed sights, where bearings are read from the position of a magnetic compass, see also article on the theodolite.
climates: division into latitude zones of the part of the earth known to ancient geographers, used by Ptolemy.
clinometer: an instrument for measuring inclination.
common hours: system of hour reckoning, see article on time and date.