ESDU Aero C.08.01.01 gives curves of rate of change with control deflection of pitching moment coefficient at constant lift coefficient in inviscid flow plotted against thickness/chord ratio for various values of the ratio of control chord to wing chord. A second graph gives curves from which the rate of change with control deflection of pitching moment coefficient in inviscid flow divided by that in incompressible viscous flow may be obtained. The curves are plotted against the rate of change of lift coefficient with control deflection in incompressible viscous flow divided by that in inviscid flow, and values for that ratio may be obtained from ESDU Aero C.01.01.03. The curves are for various values of a parameter defining the trailing edge angle of the aerofoil section; that parameter is defined by the difference between the thickness/chord ratios at 90 and 99 per cent chord divided by 0.18 times chord and so represents the tangent of an angle approximating the trailing-edge angle. It is suggested that the method may be applied to finite aspect ratio surfaces using strip theory provided the aspect ratio exceeds 4 and the sweep is small.