Mass produced since the 1930's and patented by Rex in 1947, the Model 1500 is still considered to be the best all around instrument of its kind. While other manufacturers have attempted to copy the Rex design, none can offer the quality of a Rex 1500. With its light weight and small size, the user can carry it at all times. Should it be dropped, even if not in its leather carrying case, it will not be damaged or become inoperative 99 times out of 100. Because the gauge is so durable, the Model 1500 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.