What is the sensitivity & accuracy of a spirit level or bubble vial？

Definition
Sensitivity is an important specification for spirit levels and bubble vials as it plays a big part in determining the overall accuracy of the device. The sensitivity of a level or vial is defined as the change of angle or gradient required to move the bubble by a set distance (usually 2mm). If the vial has graduated divisions then the sensitivity refers to the angle or gradient change required to move the bubble by one of these divisions (often spaced at 2mm). 
Unit       
Due to the nature of angle-measuring devices and their applications, angles are often measured in units such as degrees, minutes and seconds. 

Principles
For all spirit levels, the sensitivity specification is determined by the sensitivity of the vials that are used. This is determined by the radius of curvature within the vials, which the bubble moves across. As sensitivity increases, the level will be more precise; but the bubble will be harder to stabilize.All spirit level vials and bubble vials contain this curved radius, even though it cannot always be seen. This allows the bubble to move to the highest point of the radius as gravity acts on the liquid inside the vial once it is level. The sensitivity is directly related to the radius of curvature of the vial:
◎ The longer the radius, the more sensitive the vial will be
◎ The shorter the radius, the coarser the vial will be