Set includes: 1/16", 1/8", 3/16", 1/4" and 3/8" (1.6, 3.2, 4.8, 6.4 and 9.5 mm) thick neoprene gauges.
Simply hold the level tight against a horizontal or vertical surface. True the level and then use the thickness gauges to determine the amount out of level or plumb the surface is at that point. You can combine gauges when necessary for gaps exceeding 3/8" (10 mm).