At first when I ordered this, I thought it was for longer pieces of work. It is actually for shorter pieces. This is an add on for the Bosch Digital Protractor. What this extension allows you to do is extend it just a little bit, or as much as you need, not off the end of the leg, but rather BACK OVER THE ELBOW OF THE UNIT, to measure the angle of something that may be only 3 or 4 inches in length. By extending it the short distance, getting the angle, then deducting it from 180 degrees you can get an accurate measurement. The instructions that come with it, show you a picture of someone who is outside,holding the protractor against a wall, and extending the extension backwards across the knee to get the slope measurement of an outside window sill plate.