Thinking outside the Bento Box NPL develops a new set of calibration artefacts for areal surface topography measurement Richard Leach Engineering Measurement, National Physical Laboratory, Teddington, Middlesex TW11 0LW, UK richard.leach@npl.co.uk The world is currently on the cusp of a revolution in the way surfaces are used in manufactured products. Previously, stochastic and random surfaces, or the machining marks left by the manufacturing process, were most often used to impart functionality into the surface. More recently, deterministic patterning is being used to critically control the function of a surface. This deterministic method is the way the process of evolution has led to the creation of various functional surfaces Ȯ oft- cited examples are the lotus leaf, shark skin or eye of a fly. Examples from advanced manufacturing industry include the use of laser dimpling to reduce friction in bearings, high aspect ratio features to control the wetting characteristics of glasses, patterned topographies to enhance the adhesion of biological molecules, and so on Ȯ the list grows daily. To take advantage of the multitude of controllable functions offered by the use of structured surfaces, a measurement infrastructure is required. The latest advances made by the National Physical Laboratory (NPL) to put such a measurement infrastructure into place are described here. The measurement and characterisation of surfaces using the profile method has been used in manufacturing industry for over a century. However, whereas the profile method may be useful for showing manufacturing process change, much more functional information about the surface can be gained from an analysis of the areal surface topography. The main instruments used to measure areal surface topography are either contact (stylus) based or non-contact (optical) based. For good reasons, stylus instruments are often considered ȃreferenceȄ instruments and can achieve nanometre resolution for height measurements. However, stylus instruments require physical contact with the surface being measured, are band- limited due to their finite tip geometry and can be very slow when measuring areal surface topography. Therefore, optical instruments are becoming more popular and can overcome many of the limitations of stylus instruments. There is now a large range of commercially available optical instruments designed for surface topography measurement, for example coherence scanning interferometers (CSIs Ȯ