What Is a Bubble String Level?

The bubble string level describes the level of a bubble in a spirit level.

The bubble string level describes the level of a bubble in a spirit level during the "bubble string technique" used to determine whether two points are perfectly horizontal. It is a very common technique used in carpentry and construction.

Technique

The bubble string technique involves hanging a string between two points. A simple spirit level is then hung from the string, and both ends are adjusted until the bubble is perfectly placed between the center markings of the level.

Construction

A line spirit level is typically a glass tube mostly filled -- enough space is left for the bubble -- with a liquid with a low freezing point, such as ethanol. The tube is connected to a hook to make it easy to hang off the string. These kind of levels are designed to be lightweight so as not to sag the string too much.

Alternatives

Other methods of determining a perfect horizontal include laser levels, which projects a perfectly straight laser, and electronic levels, which digitally mimic the action of the spirit level. These often have the advantage of speed of calculation and other features, such as the accurate calculation of gradients.

References

• books.google.com: Construction Measurements - Spirit Levels
• fhwa.dot.gov: Construction Tools
• daviddarling.info: Spirit Level
• daviddarling.info: Electronic Level
• daviddarling.info: Laser Level