Hi, Can anyone tell me what this means? I'm trying to find the adiabatic expansion coefficient in order to use this air compressor calculator. http://www.engineeringtoolbox.com/horsepower-compressed-air-d_1363.html These are the variables I have at the moment..... Number of stages- 1 absolute initial pressure (psi)- 14.5 volume of compressed air at atmospheric pressure (cfm)- 20 absolute final pressure (psi)- 100. So what is this adiabatic expansion coefficient and how can I calculate for it? Thanks.