The concrete test hammer GMT HT-225A follows the measuring principle according to Schmidt and is an easy-to-use tool for testing the compressive strength of concrete. For this purpose, the concrete test hammer has an integrated spring which shoots a mass against the surface with an energy of 2.207 J. The rebound of the mass, which is dependent on the surface hardness of the concrete, can be read on the display of the concrete test hammer. By using the conversion chart, the rebound value can be converted to the compressive strength of the concrete. This simple test sequence makes the concrete test hammer well suited for on-site measurements. Before performing a measurement, use the included emery stick to smooth the surface. To minimize the impact of local variations of the concrete surface, it is recommended to take a selection of readings and use an average value. The concrete test hammer comes calibrated from the manufacturer.