A spirit level is a hollow body filled with a fluid – and an air bubble – which is used to check the horizontal position of an object. The position of the air bubble in the fluid shows the angle and the direction at which the object is inclined in relation to the horizontal level.
The hollow body containing the fluid and the air bubble has a defined radius at its top side, causing the air bubble to float to the highest point by its natural buoyancy.
The transparent upper section has markings or a circle centric to the middle position. If the air bubble is centered precisely inside the marking, the object to be checked is in the horizontal position.
Bull’s eye levels simultaneously measure the angle of inclination and the angular position, e.g. of a certain level.
Bull’s-eye levels are used to check the horizontal position of almost anything – machines, devices, appliances, instruments, etc.
The level is aligned in relation to the reference surface so that the bubble is located in the side the marking ring when the horizontal position of the contact surface is achieved.
To use a Bull's eye level on a laser (or any other item), you simply place one at diagonal corners of the chassis, and raise / lower the legs of the item until the air bubble is in the centre.