A method of determining the dimensions and location of a surface feature, for example a valve seat. The surface of the feature is measured, for example using a spiral scan path with a tactile probe and the multiple data points acquired from the scan are used to create a digitized image. The digitized image is fitted to a nominal image (e.g. CAD data) of the surface feature. The deviation of the digitized image from the nominal image is used to determine at least one of the dimensions, location and form deviation of the surface feature.