A delicate instrument used by early-day geophysical crews to measure the minute variations in magnetic attraction of subsurface rock formations. As minute variations in magnetic of the subsurface features were plotted over a wide area, the geophysicist had some idea as to where sedimentary formations that might contain oil were located in relation to non-sedimentary rocks. The forsion balance has been superceded by the less complicated (to use) gravity meter or gravimeter. See
