Sullivan's Trap Tester is designed to easily and accurately measure the pan tension on foothold traps. The tester is graduated from 1 pound to 4 pounds, in 1 pound increments. You set the foothold trap you'd like to test and press the spring-loaded tester down on the pan. The tester has black rings denoting 1 lb. increments as more pressure is applied. The trap fires against the rubber padded rod of the tester.