Abstract: Apparatus and method for obtaining an electrical signal corresponding to the enthalpy of steam expressed by Koch's state equation, is disclosed. In the form of Koch's state equation which is used, terms of minor significance are neglected and the equation is converted into a logarithmic form suitable for solution by electrical analog computer elements. A circuit arrangement comprised of adders, multipliers and function generators is disclosed for simulating and solving the potential and exponential functions in the formula for the enthalpyi = j.sub.o (t) - A.sup.. p(1/t.sup.2.82) - e.sup.(1n B .sup.+ 3 in p .sup.- 14 1n t) ,where i.sub.o is a basic quantity dependent only on the temperature t, the pressure, p, and A and B are constants.