Metric Measurements .
Understanding Vial Sensitivity
When considering vial sensitivity it is important to know that sensitivity does not reflect the accuracy of a level vial. A highly sensitive vial can be inaccurate and an accurate vial can have low sensitivity. An accurate vial will read level when in a level position.
Vial sensitivity describes how easily the vial bubble moves when shifted from its level position to an unlevel position. Bubble movement is determined by the surface inside the vial.
Sensitivity is measured in minutes and seconds. Minutes are a fraction of a degree (or angle). There are 60 minutes in one degree. This means that 1/2° is equal to 30 minutes. Sensitivity is defined as the angle the level needs to rotate to get the bubble to move 1/10th of an inch. For example, for a 20 minute vial the level must tip 20 minutes or 1/3° to move the bubble 1/10th" or 0.1". A more sensitive 9 minute vial only needs to be tipped 9 minutes or 9/60° to move the bubble 1/10th" or 0.1".
With a circular level, a 2/3° pitch will yield approximately 1/10" or 2.5mm bubble movement.
A highly sensitive vial will allow you to detect very subtle changes, which may or may not be important depending on the type of work you are doing. The real life application is that a highly sensitive vial is not good for use in general carpentry; it would take the carpenter a long time to level or plumb his work. When setting machinery or test surfaces, a highly sensitive vial is necessary to create a more precise level position.