
Jacob's staff: name for a crossstaff, especially when used for surveying, see article on the crossstaff.

Julian calendar: calendar introduced by Julius Caesar and used in Europe until the sixteenth century, or later, see article on time and date.

latitude: angle above or below the equator to indicate position on the earth. The celestial latitude, however, is an angular distance with respect to the ecliptic.

latitude plate: part of an astrolabe with a projection of altitude and azimuth lines on to the equatorial plane, see article on the astrolabe.

latitude projections: projection of altitude and azimuth lines on to the equatorial plane, see article on the astrolabe.

level: name for different types of instrument used in surveying for determining the horizontal direction and differences in height, and in gunnery and elsewhere for adjusting something to the horizontal. See also gunner's level.

level and sight: 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.

limb: the outermost part or edge of a circular or partcircular instrument carrying a scale, usually divided in degrees.

longitude: angle parallel to the equator to indicate position on the earth. The celestial longitude, however, is an angular distance parallel to the ecliptic.

lunar dial: dial where the shadow is cast by moonlight instead of sunlight, see article on the sundial.

lunar volvelle: volvelle indicating the age of the moon, which typically converts between the time indicated by the shadow of the moon on a sundial and solar time.

magic square: square grid with a number in each cell for which the sum of each row, column and diagonal is the same.

magnetic compass: instrument indicating directions by a magnetic needle, see article on the compass.

magnetic deviation: the angle between geographical north and the direction indicated by a compass needle.

magnitudes: numbers in a scale of the relative brightnesses of the stars, 1 being the brightest.

mariner's astrolabe: altitudemeasuring instrument for finding latitude at sea, having a heavy brass or bronze ring, suspended by a shackle and ring, with a degree scale and a centrallypivoted alidade.

mater: part of an astrolabe, see article on the astrolabe.

mathematical compendium: compound instrument for performing various functions in practical mathematics.

mathematical instruments: collections of instruments of assorted kinds for performing functions in practical mathematics.

measuring rod: an instrument used to measure distances or depths. See also gauging rod.

measuring rods: see measuring rod.

meridian: the plane containing the observer and both celestial poles, or containing the observer, the zenith and the pole, or, more colloquially, the northsouth line at a particular position on the earth.

meridian circle: circular scale of degrees which in use is aligned with the meridian.

mining instruments: in this period mining instruments were principally for surveying, adapted for the special conditions of working underground in mines.

nautical circle: generic term for a circular mathematical instrument of use in navigation, but likely to carry a range of mathematical and astronomical scales.

nautical hemisphere: a combination of graduated arcs and circles used for navigational calculations, see article on the nautical hemisphere.
