SOLEIL Long Trace Profiler (LTP) is a custom made instrument developed in the former LURE. As many instruments of its kind, it is based on pencil beam interferometry and uses the principle of stabilisation of the probe beam by a pentaprism equivalent reflector. The interferometer however is a polarization interferometer located close to the surface under test. The optics head can be configured to measure the optics in its working position: face up, face down or sideways. Particular care is given to absolute calibration because the precise knowledge of radii of curvature is required to determine the grazing angle and align accurately the synchrotron beamlines. A reproducible calibration procedure has been defined and checked against various reference surfaces. The main limitation to accuracy is the beam instability due to aur turbulence and thermal drifts. Careful confinement, oversampled acquisitions, and data averaging can minimize this effect. Noise is not uniformly distributed over spatial frequencies. In order to better understand the influence of beam footprint on the surface under test, and the characteristics of the beam fluctuation, we have constructed a special head where two measurements, one with a narrow pencil beam and interferometric detection and another with a large unmodulated beam and centroid detection, can be done simultaneously. The first results obtained from this device are presented here.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.