The edge tester is designed to enable the average person to accurately determine the value of any edge. Use the hard surface of the tester to complete 4 tests - providing a standard that will allow you to judge and compare edge sharpness and perfection. We focus on two of the four tests when checking our knives: 1. does the edge catch/bite into the tester or just slide down it, and at how acute of an angle and 2. pushing the cone shaped end of the tester along the cutting edge feeling for chips and nicks. You'll be able to feel any flaws in the cutting edge, as well as how smooth or toothy it is. Use with caution though - it will accentuate your OCD regarding your edges!