geometrical square: form of quadrant, with sides divided equally and having an alidade at one corner, used for measuring angles in terms of ratios in the manner of a shadow square on the back of an astrolabe.
globe dial: form of sundial, where the hour lines are on the outer surface of a sphere.
gnomon: the part of a sundial that casts the shadow for indicating the time.
golden numbers: numbers denoting the positions of years in the lunar cycle, see article on time and date.
graphometer: type of surveying instrument, see article on the graphometer.