ESDU AERO S.00.03.27 outlines, for each of the two calculations, the background theory which provides a basis for a worked example using the charts. For the isentropic expansion from rest the initial conditions define a point on the chart from which a constant entropy line is one parallel to the ordinate. From the final conditions then obtained from the chart, the energy equation from ESDU AERO S.00.03.06 yields the velocity, and the equation of continuity allows the flow area at the end of the expansion to be calculated. In the calculation of the Prandtl-Meyer expansion of a supersonic flow about a sharp corner, the energy equation is again used but in terms of the components of velocity along and at right angles to a radius vector from the corner. The initial conditions are again obtained from the charts and a series of pressure ratios is selected at each of which the specific energy and speed of sound are read from the charts at constant entropy. A numerical integration allows the angle turned by the radius vector for that pressure ratio to be calculated and from the pressure ratio and the entropy all the other conditions may be determined.