The performance of stylus profilometers can be defined by modelling their abilities to respond to sinusoidal profiles, and can be compared by mapping their limits in amplitude-wavelenyth (AW) space. The performance of traditional stylus profilometers fall within well-defined limits; but new applications are requiring new capabilities beyond these traditional limits. At low amplitudes and wavelengths the tip radius of practical styli has been a limiting factor. Development of the scanning tunnelling and atomic force microscopes has opened up this area of AW space, which extends to the resolution of individual atoms. At low amplitudes and long wavelengths, temporal stability and quality of the datum are critically important. Advances into this area of AW space, which is important to X-ray optical and other super-smooth surfaces, have been made at NPL with the Nanosurf-2 instrument. A description of the instrument and its design philosophy are given, along with examples of precision surfaces that have been measured with it.