Abstract: A frame body has a base portion for supporting a specimen and an integrally extending arm portion above the base portion for guiding a penetrating probe. Force is applied to the probe to urge it against the specimen. A portion of the frame body is in the form of a leg extending horizontally in spaced relationship to the base portion of the frame to terminate adjacent to the specimen. Reaction of the frame to applied forces causes relative movement between the base portion and the horizontally extending leg indicative of "springing" of the frame. A first electrical circuit provides a first signal proportional to the load applied to the penetrating probe. A second electrical circuit provides a second signal responsive to relative movement of the penetrating probe and supporting arm and a third electrical circuit provides a third signal responsive to relative movement between the base portion of the frame and the extending leg.