An instrument designed to measure pressure changes within rock as a result of mining operations. The instrument consists of a tongue of steel containing a groove filled with glycerin. When pressure is exerted upon the external surface of the tongue, the glycerin is partially squeezed from the groove and exerts pressure on a diaphram, which accordingly bulges outwards. A strain gage is cemented on the outer wall of the diaphragm, and as the curvature increases and the gage is strained, so does its resistance vary.