Flat jacks are used for the determination of In-situ rock stress by relief technique. The test method consists of cutting a thin slot into the surface by drilling a series of overlapping holes. The process relieves the rock surface of the stress which originally existed across it. This is measured between two points across the slot fixed in the rock prior to cutting the slot. This convergence occurring is then neutralized by inflating a flat jack fixed in the slot and the cancellation pressure is noted. Assuming that the rock mass is elastic within range of working stress, this cancellation pressure is taken as very nearly equal to the pressure that existed in the rock normal to the plane of slot before the slot was cut. HEICO flat jack equipment meets the essential requirements of IS: 7292-1974.