You can get dead-on dadoes in just three steps using this jig. The twin guide rails are custom fit to the router bit and bushing used, and can be set up by eye--no measuring. The integral clamping system is located below the jig, so it makes it easy to secure the workpiece without getting in the way of the router. The rails also act to prevent chipout along the edges of the cut. Just set the width of cut using a scrap of the workpiece that will eventually be fit into the dado, align the rails, lock it down, and rout. Perfect dadoes, every time.

From Fine Woodworking #226