The Impact-Echo is used for nondestructive evaluation of concrete and masonry, based on impact-generated sound waves. Waves move through structure and are reflected by internal flaws and external surfaces. Can measure thickness of slabs, to determine the location and extent of cracks, de-laminations, voids, honeycombing and de-bonding; and can locate voids in the sub-grade directly beneath slabs and pavements. Impact-Echo is not adversely affected by the presence of steel rebar. Available in two configurations, System A has single hand-held transducer while System B has two transducers separated by a fixed distance for independent measurements of wave speed.