ESDU Aero W.00.03.01 gives theoretically-derived curves of critical Mach number plotted against thickness/chord ratio for a range of lift coefficients from zero to 0.5, and for an elliptic cylinder at zero lift. The curve for an elliptic cylinder at zero lift is given to provide an upper bound because such an aerofoil for a given thickness/chord ratio would have the lowest suction peak and hence the highest critical Mach number but it is not a practical section shape. The curves apply to cambered aerofoils designed for the highest critical Mach number at the chosen lift coefficient and do not relate to aerofoils operating at off-design conditions. The relationship between the critical Mach number and the Mach number for shock-induced separation is discussed.