![]() For a precision machinist level with 2 mm (0.079 in) divisions, when the vial is tilted one division, the level will change 0.0005 in (0.013 mm) one foot from the pivot point, referred to by machinists as 5 tenths per foot. 2 mm (0.079 in) is the usual spacing for graduations on a surveyor's level, the bubble will move 2 mm (0.079 in) when the vial is tilted about 0.005 degree. If the bubble housing has graduated divisions, then the sensitivity is the angle or gradient change that moves the bubble by one of these divisions. The sensitivity of a level is given as the change of angle or gradient required to move the bubble by unit distance. Sensitivity is an important specification for a spirit level, as the device's accuracy depends on its sensitivity. This is done in two horizontal perpendicular directions. In this latter case, the plane of rotation of the instrument is levelled, along with the spirit level. ![]() A difference implies that the level is inaccurate.Īdjustment of the spirit level is performed by successively rotating the level and moving the bubble tube within its housing to take up roughly half of the discrepancy, until the magnitude of the reading remains constant when the level is flipped.Ī similar procedure is applied to more sophisticated instruments such as a surveyor's optical level or a theodolite and is a matter of course each time the instrument is set up. If the level is accurate, it will indicate the same orientation with respect to the horizontal plane. The spirit level is then rotated through 180 degrees in the horizontal plane, and another reading is noted. This reading indicates to what extent the surface is parallel to the horizontal plane, according to the level, which at this stage is of unknown accuracy. ![]() The level is placed on a flat and roughly level surface and the reading on the bubble tube is noted. To check the accuracy of a carpenter's type level, a perfectly horizontal surface is not needed. It serves to level a surface across a plane, while the tubular level only does so in the direction of the tube. A colorant such as fluorescein, typically yellow or green, may be added to increase the visibility of the bubble.Ī variant of the linear spirit level is the bull's eye level: a circular, flat-bottomed device with the liquid under a slightly convex glass face with a circle at the center. Alcohols also have a much wider liquid temperature range, and will not break the vial as water could due to ice expansion. Alcohols have low viscosity and surface tension, which allows the bubble to travel the tube quickly and settle accurately with minimal interference from the glass surface. Where a spirit level must also be usable upside-down or on its side, the curved constant-diameter tube is replaced by an uncurved barrel-shaped tube with a slightly larger diameter in its middle.Īlcohols such as ethanol are often used rather than water. At slight inclinations the bubble travels away from the marked center position. They have a slight upward curve, so that the bubble naturally rests in the center, the highest point. These vials are incompletely filled with a liquid, usually a colored spirit or alcohol, leaving a bubble in the tube. Different types of spirit levels may be used by carpenters, stonemasons, bricklayers, other building trades workers, surveyors, millwrights and other metalworkers, and in some photographic or videographic work.Įarly tubular spirit levels had very slightly curved glass vials with constant inner diameter at each viewing point. ![]() A spirit level, bubble level, or simply a level, is an instrument designed to indicate whether a surface is horizontal (level) or vertical ( plumb).
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