The C555 is useful in assessing the dryness in the top ½ inch of smooth concrete slabs. When paired with the Rapid RH testing system by Wagner, the C555 is an excellent support to provide extra data and save time. In this case, the C555 should be used whenever you want to begin assessing a slab of concrete. This way, you can properly determine where to place your RH sensors. We truly believe that the C555 can best suit your needs when bundled with the Rapid RH system. Here are some other times when you should use a C555: