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.