
equinox: either of two points on the celestial sphere where the equator meets the ecliptic, representing the position of the sun when it is 90 degrees from the poles, or the two dates in the year when the sun is in this position in its annual cycle.

folding rule: see rule.

folding rule and level: a compound instrument combining the functions of both a folding rule and level.

gauging rod: measuring stick, usually with a scale to provide a direct reading of volume, such as the liquid content of a barrel, or the weight of a cannonball.

geographical astrolabe: form of astrolabe, where the lower plate is projected for the earth, while the rete includes the ecliptic.

geographical planisphere: map of the earth, produced by geometrical projection of a sphere on to a flat surface. Included as the more prominent part of the geographical astrolabe.

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.
