Third generation synchrotron X-ray sources such as the European Synchrotron Radiation Facility and the Advanced Photon Source (USA) have made very intense beams of very high energy X-rays available for the first time. At energies in excess of 60 keV penetration lengths of the order of centimetres are possible in most engineering materials. The associated low scattering angles limit the strain measurement directions available at depth. Gauge dimensions as small as microns and sub-second measur...