The Rex QC-D Type D Vernier Scale Durometer for Hard Rubber and Plastics is so durable, the QC comes with a lifetime guarantee. The key to the gauge's durability is its sliding vernier scale- there are no cams, gears, or levers to wear out. This vernier scale holds the maximum reading, and is especially useful for testing in hard to reach areas. The vernier scale is marked in increments of 5 points, and with a little practice, one can obtain readings to within 1 point.