Machinist levels provide greater accuracy than common construction levels. These levels must be used when the variability of the reference plane is within the range of the level's sensitivity. Otherwise, measurements will continually be "chased," making these precision levels more difficult to use. Vials are filled with a high grade mineral oil to resist thermal expansion and contraction and excessive bubbles. mitigate multiple bubbles during handling, and remain safe in the event that a level is damaged. A notch is offered in it's precision ground base so that the level may be placed on a minimum arc or diameter.