Spirit level

 

— perhaps the most famous and common type of building levels: a tool that uses a sealed flask with an air bubble inside as a scale. By the position of the bubble, the presence of deviations from the horizontal, vertical or other angle is determined (depending on the capabilities of the device — see "Measuring capsules"); and on the walls of the flasks there are usually markings that make it easier to work with the tool.

Note that bubble flasks may also be provided in other types of measuring instruments; in this case, we mean levels that do not have any other measuring devices, except for such flasks.