ESDU Aero W.S.02.04.12 gives curves for the skin friction drag coefficient of a flat plate plotted against the fraction of the plate for which the boundary layer is laminar for values of freestream Mach number up to 5. Sets of curves are given for Reynolds numbers of one million, ten million and a hundred million. These curves should only be used in conjunction with ESDU Aero W.S.02.04.13, and, for more recent information concerning skin friction and other parameters for laminar and turbulent boundary layers on a smooth flat plate, ESDU 68019 and ESDU 68020 should be consulted.