There is no such thing as a room with perfect 90° corners. When it comes to setting an angle on your mitre saw for skirting or cornice, the SM-KS makes all other protractors and angle measuring devices obsolete. The SM-KS is elegantly simple, reliable, and effortlessly accurate. It automatically bisects the angle for you, internal or external; you will never have to peer at another protractor scale. All you need do is place the SM-KS on your mitre saw table and line the blade up. The SM-KS saves you time by getting the correct angle first time, you will never have to re-cut a piece again.