Johnson's 40-6675 3-Dot Laser is designed for both professional tool users and homeowners. This Self-Leveling 3-Dot Laser projects three simultaneous laser dots allowing the user to establish a perfect plumb line from floor to ceiling. The 3-Dot Laser eliminates the need for time consuming plumb bobs and allows one man to do the job of two. Self-leveling means the tool is a quick set-up. There are no adjustments required. This is a perfect tool for locating lights & sprinkler systems in ceilings. It is also useful for carpenters and drywall installers when building walls as it allows a fast and accurate vertical/plumb reference point. The 3-Dot Laser's co-molded rubber housing assures its durability. The internal components of the 3-Dot Laser are securely locked into place when the tool is not in use. This locking compensator not only protects the internal components but assures the tool's accuracy.