level-¹Horizontal. ² A leveling instrument. ³ An attachment (such as a spirit
level) to indicate when an instrument or other device is level or vertical.

level—In mining, a horizon along which the mining of an ore body is performed. It includes all drifts, cross cuts, and other horizontal workings on any one horizon or level.

level, Abney—A hand level with a rotatable vertical circle to which a bubble is attached. It can be used to measure vertical angles.

level, automatic—See level, pendulum.

level, bull\’s eye—See level, circular.

level, circular—A spirit level with the inside surface of its upper part ground to spherical shape; the outline of the bubble formed is circular and the graduations are concentric circles. Used where a high degree of precision is not required, as in plumbing a level rod or setting an instrument in approximate position. Also referred to as “universal level” or “bull’s eye level.”

level, dumpy—A leveling instrument which has its telescope permanently attached to the leveling base, either rigidly or by a hinge that can be manipulated by a micrometer screw.

level, electronic—A rotating laser level which establishes a level beam at a known elevation.

level, grade—A rotating laser level which can establish a level beam at a known location and slope. It can also be turned on its side to provide a vertical reference.

level, hand—A hand-held instrument for approximate leveling. It consists of a sighting tube with a split field of view; a horizontal crosshair in one-half of the field bisects the image of a spirit level in the other half, when the instrument is held level.

level, pendulum—A leveling instrument where the line of sight is automatically maintained horizontal by means of a built-in pendulum device.

level, prism—A type of dumpy level in which the level bubble can be viewed front the eyepiece end by means of an attached prism, at the time the rod is being read.

level, rod—An accessory for use with a level rod or a stadia rod to make certain of a vertical position. The rod can have one circular vial or two placed at right angles when in use. Both types are mounted against the rod.

level, rotating laser—A leveling instrument utilizing a rotating-beam laser.
Used in construction in place of chalk lines, plumb bobs, and the like.

level, self-leveling—See level, pendulum.

level, spirit—A closed glass tube (vial) of circular cross section. its center line also forming a circular arc, its interior surface being ground to precise form; it is filled with ether or liquid of low viscosity, enough free space being left for the formation of a bubble of air and gas.

level, striding—A spirit level so mounted that it can be placed above and parallel with the horizontal axis of a surveying or astronomical instrument, and so supported that it can be used to measure the inclination of the horizontal axis to the plane of the horizon.

level, tilting—A leveling instrument, generally of the dumpy type, in which the final leveling of the telescope is obtained by small controlled amounts of rotation of the telescope about a horizontal axis.

level, universal—See level, circular.

level, wye (Y)—A leveling instrument having the telescope, with attached spirit level, supported in wyes (Vs). The telescope can be rotated about its longitudinal axis (collimation axis) in the Y’s and it can be lifted and reversed, end for end. The instrumental adjustments made possible by this mounting are peculiar to the instrument. This level forms one of the two general classes of leveling instruments, the other class being represented by the dumpy level.

level circuit—The measurement of bench mark elevations by spirit leveling in two different directions from one end of the circuit to another. Different turning points are used in each of the two different directions.

level circuit, double rodded—See level circuit, simultaneous.

level circuit, multiple—More than two measurements of elevation by spirit leveling along different routes between the same terminal points.

level circuit, simultaneous—The circuit of spirit levels measured between two terminal points composed of two separate turning points for computing the height of instrument at each successive setup. Also called “double rodded level circuit.”

level constant—¹ The amount by which the actual line of sight through a leveling instrument departs (when the bubble is centered in the vial) from the truly horizontal line through the center of the instrument. ² See C-factor.

level control—A series of bench marks or other points of known elevation, established throughout a project.

level error—The angle between the horizontal axis of a telescope’s mounting and a horizontal plane through the mounting.

level surface—A surface which at every point is perpendicular to the plumb line or the direction in which gravity acts. A level surface is an equipotential surface. *the surface of a body of still water is a level surface. See leveling, water surface of the ocean – if changes caused by tides, currents, winds. atmospheric pressure, etc., are not considered – is a level surface. The surface of the geoid is a level surface. Any line lying in a level surface is a level line. In a survey of a limited area, a level surface is sometimes treated as a plane surface. Level surfaces are approximately ellipsoidal in shape, the distance between any two level surfaces decreasing with increase of latitude. For example, a level surface which is 1,000 m above the mean surface of the sea at the equator is 995 m above that surface at the poles.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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