code: def _dPdT_sat(cls, T):
          
          Tita = 1-T/cls.Tc
          suma1 = 0
          suma2 = 0
          for n, x in zip(cls._Pv["ao"], cls._Pv["exp"]):
              suma1 -= n*x*Tita**(x-1)/cls.Tc
              suma2 += n*Tita**x
          Pr = (cls.Tc*suma1/T-cls.Tc/T**2*suma2)*exp(cls.Tc/T*suma2)
          dPdT = Pr*cls.Pc
          return dPdT
docs: Auxiliary equation for the dP/dT along saturation line
  
          Parameters
          ----------
          T : float
              Temperature, [K]
  
          Returns
          -------
          dPdT : float
              dPdT, [MPa/K]
  
          References
          ----------
          IAPWS, Revised Supplementary Release on Saturation Properties of
          Ordinary Water Substance September 1992,
          http://www.iapws.org/relguide/Supp-sat.html, derived from Eq.1