Introducing the L Square Ruler Bubble Leveler (3-piece) Set by POWERTEC. These handy tools were designed to help improve your workflow by providing you with highly accurate measurements and proper alignments - eliminating much of the guesswork involved with common woodworking and other high precision task. Commonly referred to as framing squares or carpenter's squares, this upgraded version also possesses built-in bubble levelers for proper placement and level measurements. Included Ruler Sizes: 5-3/16 in. 8-3/4 in. 14-5/8 in. Each Ruler Features: Standard and Metric Systems of measurements. Additional Specifications: Bubble Vial Positions: 90° Graduations: 1/16 in., 1/8 in., 1 in., 1 mm, 1 cm.【The squares are factory set, if after checking, you find them to be out of square, the two large squares are adjustable and can be reset. 1. Use a square or set block of known accuracy, to check the larger squares for perpendicularity. If not perpendicular, loosen the screws on the handle and adjust until the ruler is perpendicular to the square. While holding the ruler against the square, tighten the screws. 2. If there is no square available, the right angle accuracy can be checked by using the factory edge of a board. Using the factory edge, draw a line and then flip the square ruler over and draw the same line from the other direction. If the 2 lines are apart, use a 3mm wrench to adjust the angle. Repeat the steps until the 2 lines overlap.】. Material: Aluminum.