Performance of roughness measuring instruments is best compared by using Stedman diagrams. These make clear why the majority of roughness measurements for inspection and quality control in engineering industry are still made with stylus instruments. The design and construction of these instruments is described and compared with their predecessors, and their advantages, limitations and sources of error are discussed. The use of computers with modern stylus instruments raises problems of signal conditioning such as analogue-to-digital conversion and form and waviness removal. The former requires control of quantisation and aliasing, while the latter needs the design and implementation of specialised filters such as the robust Gaussian and valley removal filters. Characterisation of profile measurements includes both amplitude and texture parameters; functions such as probability distributions, autocorrelation functions and power spectra are also sometimes used, but their drawbacks need to be realised.  Special amplitude parameters have been developed to describe the multiprocess surfaces now in common use. Roughness parameter specification in standards raises questions of sampling robustness. Applications are illustrated by case histories from fluid dynamics, heat transfer and automotive engineering.