Jig makes for quick adjustment of circle cutter
Cut a piece of 3⁄4 x 11⁄2 " stock to a length equaling the maximum diameter of your circle cutter. Mark a line across the width of the block at its midpoint, and drill a 1⁄4 "-deep hole with the pilot of your circle cutter at the center of this line. Then, apply two strips of measuring tape. (You can buy the tape from many hardware stores and catalogs. Apply just one strip if your cutter has only one blade.) To get a precise reading of your circle cutter's radius, lower the pilot into its hole and align the cutting point with the rule measurement.
—From the WOOD magazine shop