Abstract: To measure compressions and settlements in the foundations of heavy structures, a continuous loop of tubing is installed within the foundation of the structure, with the open ends of the loop brought to a convenient, accessible terminal point. A liquid interface between a heavy density fluid and a light density fluid is moved through the tubing, the particular fluid on either side of the interface being continuous back to the terminal. The pressure difference resulting from the difference in densities of the two fluids, and the changes in height between the fluid interface within the tubing and the constant upper surface of the driving heavy density fluid in the terminal, is sensed by a pressure transducer fitted within the terminal to the light density fluid in the discharge leg of the loop.