Angle finders use two arms hinged to a protractor to read angles between two points on both inside and outside corners. Dial and digital protractors, operating a 180-degree axis, are used to display the angle between the two points, with digital protractors being easier to read. When using an angle finder, the surface you are checking must be free of high spots and debris and the protractor arms must be straight to ensure a correct reading.

Loosen the centre locking nut located where the arms of the angle finder meet at the protractor.

Extend the angle finder until the protractor reads 180 degrees. Examine the arms of the angle finder to ensure they are straight. If you find the arm(s) of the angle finder are bent, replace the angle finder. Straightening the arms will not ensure a correct measurement.

Push the arms of the angle finder into a corner of your home. Read the angle dimension aligned with the straight line etched on the surface of the protractor or read the digital display. Move the angle finder to another point on the corner and check the angle displayed by the protractor. Measuring the angle at multiple points reduces misreadings from uneven material.

When measuring outside corners the protractor will display a large measurement---subtract this from 180 to determine the degree. For example, a reading of 135 subtracted from 180 degrees would mean a 45-degree angle.

Wipe the angle finder with a clean rag. Apply a light coating of penetrating oil to a metal angle finder before storing to ensure the angle finder is in proper working condition when you need it.