A profile measuring machine has been developed for use in the production of X-ray optical mirrors, and its configuration permits the internal measurement of open-ended cylinders. It has been designed to provide for rapid measurement and evaluation of the figure of both ground and polished surfaces. Typically, the shallow curves being measured have lengths of up to 200 ram and sags of a few mm, and positions on the curve are measured with resolutions of 1 μm and 80 nm in the respective directions. The axial position is measured by a Moire fringe grating system, and the sagittal position by a He-Ne laser interferometer which monitors the separation of the stylus head from a non-load-bearing reference straight edge which is referred directly to the work being measured. A tight metrological loop confers high immunity from the effects of environmental vibration. Measurements in the two axes are simultaneously transferred into buffer stores, and then processed to provide output in both analogue and digital forms, the latter permitting further rapid data processing. The ability to measure rapidly and accurately in a workshop environment has greatly facilitated the efficient production of X-ray optical mirrors. This philosophy is equally relevant to other areas of optical and precision surface measurement.