This is a time saving tool for setting your tool heights. Place the magnetic sensor on the table or part, connect the alligator clip to your tool, and move the tool until it contacts the sensor. The tool will then retract exactly 1". You now know the exact distance from your cutter to your table or part. Very handy for setting up a numbered tool library. Has a nice plug in connection so you can remove it and keep it in a drawer when not in use. Takes a few minutes to install and set up mach 3. Comes with CD, decal and easy to follow instructions.