The essential features of a top quality spirit level are the vials which should be shockproof and virtually unbreakable, and the method of fixing the vials into the body so that they cannot work loose. The body should be tough, robust and stable and the working faces should be accurately ground.
An accuracy tolerance of ± 1mm per metre or 0.057° is often quoted.
This tolerance indicates that the work will not be more than a maximum of 1mm per metre out of true if it has been levelled with the bubble central between the two gauge lines. Expressed another way, if a 1 metre level is lifted by 1mm at one end then the included angle at the other end would be 0.057° against the horizontal.
A precision instrument based on a series of optical mirrors, one of which is pendulum mounted.
A horizontal datum can be established by matching a split image of a target mounted on a calibrated staff.
The rise and fall of land can be measured as well as establishing level points and gradients.
These are often used by scaffolders.
Box section body levels are traditionally used by carpenters and bricklayers as they are easy to clean. Traditionally made from tubular box section aluminium.
These levels are canoe shaped to fit easily into an overall pocket without tearing the material.
Digital levels present objective positive data on an LCD.
A transducer electronically measures the angle of inclination. The interpreted signal can be displayed in degrees, percentage slope or pitch, accurate to 0.1° over a 360° measuring range.
A girder section body level with hand holes is traditionally used by bricklayers for ease of handling with wet hands.
A laser level is a spirit level with a built-in laser module which extends greatly its range by emitting a concentrated beam onto a target surface.
The accuracy of a laser level relies on both the resolution of the spirit vials and the module being set parallel to the reference surface. A laser beam resolution of 0.25mm/m (0.015°) is better for exterior use over distances.
A power output of maximum 1 milliwatt (<1mW) ensures that laser levels are classified under BS (EN) Class II safety standards.
One should not look directly into a laser beam.
All levels carry a warning to this effect.
Line levels are small, lightweight, and are for use with builder's lines.
Magnetic base levels are for use on ferrous materials where the level can be attached to the material so that the material may be adjusted with both hands.
Generally made from Die-cast aluminium. Magnetic models are available.