Particle ratios at SPS, AGS and SIS
  Ratios of integrated particle yields provide the best method for determining the temperature and the chemical potential. The chemical freeze-out parameters obtained at CERN/SPS, BNL/AGS and GSI/SIS energies all correspond to a unique value of 1 GeV per hadron in the local rest frame of the system, independent of the beam energy and of the target and beam particles. 
J. Cleymans, H. Oeschler and K. Redlich