This Demonstration compares two adiabatic compressors or turbines with different efficiencies. Air, which is assumed to be an ideal gas, is either compressed or expanded. Select “compressor” or “turbine”, and select whether to “compare at the same outlet pressure” or “temperature” using the buttons. Select the outlet pressure or temperature, and select the efficiency of each turbine or compressor with sliders. The efficiency is relative to a reversible turbine or compressor.