The upper image is a plain precision level used in the engineering field to level machines or workpieces, the lower image shows an adjustable precision level that has an accuracy of 1:10000. The adjustable nature of this level can also be used to measure the inclination of an object.
The accuracy of a spirit level can be checked by placing it on any flat surface, marking the bubble's position and rotating the level 180°. The position of the bubble should then be symmetrical to the first reading.
Both levels have a "vee" groove machined along the base which enables the level to sit on a round bar while remaining parallel with the bar's axis. They also have a smaller cross level to enable the second axis to be roughly checked or corrected.
While a precision level may be used to check and correct the twist in a machine (or workpiece), its presence does not necessarily need to be corrected.