Carpenters should have at least a line level, a 9-inch torpedo level, and 2-foot and 4-foot carpenter's levels.
The torpedo level has three vials with readings for level, plumb and 45. To protect the bubble on a torpedo level, cut a slit in a small piece of garden hose and place it over the bubble.
The carpenter's level is a multipurpose level that measures level and plumb and provides a straightedge. Carpenter's levels come in different lengths, from 2 inch to 6 inch.
The post-and-pipe level is designed for hands-free use. It's strapped onto a post with rubber bands to determine plumb.
The bull's-eye level was also intended for hands-free use. Its straps hold it securely to round, square or irregular shapes.
The line level is used to measure long distances or to install chair molding. It's used by clipping two hooks taut on a piece of contractor's line and adjusting the string until the bubble is level.
The digital laser level is self-calibrating. To use it, point its laser at the surface that is being leveled. The laser will flash until the surface is moved to a perfectly level position. At that point the laser will stop flashing, and the digital reading will indicate that the surface is level.
Homemade levels can be just as effective as purchased ones. Place a marble at the center of the work piece and at other spots along the surface. If it doesn't roll in any direction, the piece is level.
Another homemade level can be made with colored water inside a bowl with horizontal rings around it. Place the bowl of water on the surface. The surface is level when the water is level with the rings.