Consists of two sturdy, rotating, plastic
disks that are joined together. Rounded tips are spaced at standard testing intervals from 1 to 15 mm apart. A 20 and 25 mm spacing also are given. One disk setting tests from 1 to 8mm, and the other setting tests from 9 to 15 mm. To change settings, just rotate the top disk until it clicks in place. Includes instructions and carrying case.