A strain gage transducer system has been developed which functions as ’’electronic calipers’’ to measure changes in thickness of samples as they are compressed in an opposed diamond‐anvil optical cell. Planimeter measurements on photomicrographs of the same samples determine area changes and ruby fluorescence techniques provide pressure measurements. These techniques permit direct volume change measurements to be performed in the diamond cell. Accuracies inv/viof 1% or better provide experimental PVT data to assist in developing equation of state models for explosive materials.