The Generalized Lee-Kesler Charts essentially present the values of Z₀ and Z₁ obtained by the above procedure as function of T_r and P_r (as). A variety of other thermodynamic variables can also be computed in an identical manner. Examples include residual enthalpy and entropy, and gas fugacity. These properties are presented either in the form of figures or charts (see, for example, Appendix E of J.M. Smith, H.C. Van Ness and M.M. Abbott, Introduction to Chemical Engineering Thermodynamics, 6th ed., McGraw-Hill, 2001).