Test Systems for Tablets Concrete Thickness Gauge (CTG-2) Save thousands by using our CTG-2 based on the Impact Echo test method with proven 2% accuracy in comparison studies. Foundation Test Gauge (FTG) Measure the depth and integrity of drilled shafts, driven piles, concrete mats, and timber foundations. Resonance Test Gauge (RTG) Connect to any Windows device and the calculating is done for you. Accurate results in under a minute on concrete, asphalt, rock, etc.