ESDU 09016 provides a method@ based on that of van Driest and Blumer@ which enables the required height of roughness elements in a boundary-layer transition band to be estimated from the local boundary-layer displacement or momentum thickness@ together with conditions at the edge of the boundary layer. The item is accompanied by a GUI-based program which@ when used in conjunction with a coupled integral-boundary-layer aerofoil or wing /body code (e.g. VGK or VFP)@ permits rapid evaluation of the required roughness height over a range of test conditions. The program also provides the option determine the required roughness height to fix transition on a simple equivalent flat plate.