The higher the sensitivity the more precise the spirit level is. This means that the bubble of a more precise spirit level reacts more when one end of the spirit level is lifted.
For craftsmen different tasks call for different degrees of precision. This is why professionals often have more than one spirit level, to get different rates of vial sensitivity. A spirit level with standard sensitivity is easy to work with and often good enough. But more demanding tasks call for a spirit level with higher sensitivity.
The vial shape
Higher and lower sensitivity is achieved by changing the shape of the vial. If we take a closer look at a vial we can see that it has a barrel-shaped inner contour. Within the barrel-shape the air bubble searches for the highest point. Had the vial been a straight tube, with no curve, it would have been impossible to level.
Less curve, faster reaction
The curve of the vial can be looked upon as a sector of a bigger circle. The radius of that circle determines how curved the vial is, and therefore how sensitive it is.
A larger radius means that the bubble can move more easily and reacts to smaller movements.
Which sensitivity do you need?
Sensitivity is measured in mm per meter. The rate is based on a spirit level 1 meter long, and how high one end of the level must be lifted for the bubble to move 2 mm.
Ten times as sensitive
The standard for most spirit levels on the market is a sensitivity of 10 mm/meter, the equivalent of a 200 mm radius. Hultafors also offers spirit levels five and ten times as sensitive than standard.