PECO 77114 Pocket Penetrometer Spring-operated penetrometer is used to measure compressive strength of soil by pushing a ground and polished 1/4” diameter loading piston into soil to a depth of 0.25”. End area is 0.05 square inch. Compressive load in tons per square foot or kg per square cm is indicated by reading scale on piston barrel. Maximum reading reach is shown by friction ring. Made of anodized aluminum. Allen wrench and plastic carrying case with belt loop are included. 6-1/4” Long.