The Wagner Meters C555 Concrete Moisture Meter is an effective tool to target pockets of unusually high or low moisture in the concrete slab before placing Rapid RH L6 Smart Sensors. The C555 Concrete Moisture Meter is fully compliant with ASTM F2659 for preliminary evaluation of the comparative moisture condition of concrete, gypsum cement, and other floor slabs and screeds. The C555 emits a signal into the material to measure moisture down to ½ inch below the surface. Sure, the C555 is a pretty good tool for wet/dry indications on its own. But, when used with the Rapid RH testing system, the C555 Concrete Moisture Meter becomes an effective targeting system that helps you place your L6 Smart Sensors in the areas where they will be most effective.