|conjunction: two planets having the same position (in longitude) in the ecliptic are said to be in conjunction. This relative position had important astrological significance.
|cross-staff: instrument for measuring angles between distant objects, mostly altitudes, see article on cross-staff.
|cross-staffs: see article on cross-staff
|crucifix dial: form of polyhedral sundial in the shape of a crucifix, see article on sundial.
|cylinder dial: type of altitude dial, see article on the sundial.
|declination: angle above or below the celestial equator.
|declinatory: instrument used in constructing a sundial, to find the declination of a plane.
|degrees: the conventional divisions of a circle, one being the 360th part of a circle, and thus the units used to measure and express angles.
|diagonals: lines used in the subdivision of divisions of an arc, also known as transversals. Each diagonal line is drawn across the division from its beginning to its end, and is divided linearly either by dots or by concentric arcs. In this way the linear division of a line can be used for the angular subdivision of an arc.
|dial: instrument for telling time by the position of the sun (occasionally by the moon), see article on the sundial.
|dialling quadrant: instrument in the form of a quadrant used in the construction of a sundial.
|diptych dial: type of sundial which, in many cases, could be called an astronomical compendium, in the form of a folding tablet, usually in ivory, with at least a string gnomon and a horizontal dial on the inside, but often with other dials as well.
|disc dial: type of sundial belonging in the class of altitude dial.
|dividers: instrument with jointed legs for measuring and transferring distances, see article on the dividers.
|dominical letter: letter denoting the day of the first Sunday of the year, see article on time and date.
|drawing instruments: instruments used for drawing and constructing geometrical figures, see article on drawing instruments.
|Easter table: table for calculating the date of Easter, see article on time and date.
|ecliptic: line on the celestial sphere representing the annual path of the sun through the stars.
|epacts: numbers used in the calculation of Easter, see article on time and date.
|equal hours: system of hour reckoning, see article on time and date.
|equator: circle on the earth's surface 90 degrees from the poles, or the circle on the celestial sphere 90 degrees from the celestial poles.
|equatorial: relating to or based on the equator. Has much the same meaning as equinoctial.
|equatorial dial: another name for equinoctial dial.
|equatorium: instrument to determine the longitude of one or more of the planets at any given time.
|equinoctial: relating to or based on the equator, or relating to the equinox.
|equinoctial dial: sundial where the hour plate or circle is set parallel to the equator, see article on the sundial.
|equinoctial ring dial: type of sundial, included as an equinoctial dial, comprising two pivoted rings and a bridge for adjusting for solar declination, or of three rings.
|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.
|graphometer: type of surveying instrument, see article on the graphometer.
|gunner's caliper: a instrument used to take dimensions in gunnery, such as the diameter of cannons and projectiles.
|gunner's compendium: an instrument combining several functions required by the gunner, often incorporating the gunner's sight and gunner's level, along with additional elements.
|gunner's folding rule: a folding rule carrying tables or scales specially adapted for the use of gunners.
|gunner's gauge scales: scales which provide the weight of a sphere (the shot) from a measurement of its diameter; in gunnery these scales were traditionally provided for iron, lead and stone.
|gunner's level: instrument used to set the elevation of a large gun, see article on the gunner's sight and level.
|gunner's rule: see rule.
|gunner's sight: instrument used to elevate and aim a large gun, see article on the gunner's sight and level.
|gunner's sight and level: instrument used to set a large gun to the horizontal, or to elevate and aim it on a target, see article on the gunner's sight and level.
|gunnery instrument: see gunner's compendium.
|hodometer: device for measuring distance by means of a wheel, pushed along the ground, attached to a geared movement with a dial or other form of distance register.
|horary quadrant: quadrant used to tell the time, usually from a measure of solar altitude, see article on the quadrant.
|horizon obliquus: line denoting the local horizon on an astrolabe latitude plate, see article on the astrolabe.