Abstract: In order to measure the surface profile of a workpiece, a yoke having two fixed feet is held in contact with the surface as the workpiece is rotated. A dynamic probe is mounted on the yoke by means of a transducer which outputs a signal dependent upon the position of the dynamic probe relative to a transducer datum. The fixed feet and the foot of the dynamic probe have a similar shape and size so that they detect irregularities in the workpiece surface with equal sensitivity. Fourier analysis of the signal caused by movement of the dynamic probe directly by the workpiece and also by movement of the yoke enables the profile of the workpiece to be determined. In order to improve the frequency response of the transducer output over the range of harmonics considered, the angles between the dynamic probe and the fixed probes are unequal. The apparatus does not require a precision spindle type machine to rotate the workpiece and is therefore particularly suitable for in situ measurement of workpiece profiles.