The Blind Mark: Arc Mark - The Five Easy Steps

Step 1 Place the Arc Mark Target, with the magnet face pointing down, in recessed light fixture. For the 6" inch recessed light fixtures locate the target over the head of the assembly screw which is located in the center of the recessed light fixture adjacent to the rafters. Make a mental note of the orientation of the Arc Mark Target relative to the direction of the rafters.
Step 2 Once the Arc Mark Target is installed in the recessed light fixture, cover the recessed light fixture with the drywall. Position your drywall in the exact location and fasten it with enough drywall screws to make it secure.
Step 3 With the magnet face on the Arc Mark Locator facing up, pass the Locator across the area in which the Target is located. Try to keep the Locator in about the same orientation as the Target. Find the Target and snap in place. Do not force the Target locator into position. Hold the ides of the Locator and let it jump to final position on its own. Then, take your pencil and mark the outside radius of the Locator.
Step 4 Remove the Arc Mark Locator from the drywall. With a quadrant of the circle marked, visualize the entire circle. With your spiral saw plunge the tip of the bit cutter into the drywall on the outside of the line at the middle of the line. Move the tool slowly towards the center and counterclockwise 360 degrees around the recess light fixture.
Step 5 Finally, remove the drywall cut out and the Arc Mark Target.