A rebound hammer, also known as a Schmidt hammer, is a non-destructive testing device used to assess the surface hardness and compressive strength of concrete and rock surfaces. It works by delivering a calibrated impact to the surface and measuring the rebound distance of a plunger, which correlates to the material's hardness and strength. The rebound number obtained from the test provides an estimate of the concrete's compressive strength, allowing engineers to quickly evaluate the quality of existing structures without damaging them. This method is widely used in field testing due to its simplicity, speed, and cost-effectiveness, although it is generally considered as a supplementary test to more detailed laboratory analyses.