Spirit levels are available as bull’s eye, horizontal or cross spirit levels.
The bubble in a bull’s eye level simultaneously indicates the direction and the angle of inclination in the horizontal plane.
Horizontal spirit levels only indicate the angle of inclination along the spirit level axis, with no indication of the overall inclination or its direction with respect to the horizontal plane.
Cross spirit levels contain two horizontal spirit levels situated at a 90° angle to each other. This allows them to simultaneously indicate the direction and angle of inclination, with separate indication of the X and Y components.
The hollow body containing the fluid and the gas bubble has a defined radius at its top side, causing the gas bubble to float by its buoyancy always to the highest point.
The transparent upper section normally carries markings or a circle centric to the middle position. If the gas bubble is centered precisely inside the marking and if the air level is properly adjusted, the object to be checked is in the horizontal position.
The sensitivity of spirit levels is given as angle of inclination, e.g. 30 angular minutes or 0,5 degrees. This is the angle of inclination by which the spirit level must be tilted to make the bubble move by 2 mm. A spirit level with a sensitivity of 6 angular minutes therefore has a higher sensitivity than a spirit level with a sensitivity of 30 angular minutes.
Sensitivity is sometimes also given in millimetre per metre, i.e. as difference in altitude per unit of length.
See also the reference table opposite.
|Difference in altitude||Angle w||Angle w|
|in millimetre per metre||in angular minutes||Degree, decimal|