Laying out square lines is an important part of many home improvement projects like laying ceramic tile…but a typical squaring tool is only accurate for a few inches so how do know they’re square? Try this. Establish one line parallel to a wall and mark off 4 feet on it. Then measure out 3 feet perpendicular from one end of the line and make a temporary mark. By completing the triangle with your tape measure and insuring that the two end points are 5 feet apart, you have created a right triangle. That means that the first 2 lines will be exactly perpendicular, or square. If this all sounds familiar it’s because it relies on the Pythagorean Theorem from your junior high geometry class…. A² + B² = C²…..and you thought you’d never use this stuff.