A measuring apparatus, for measuring the distance to a surface having fluctuating reflectivity, the measuring apparatus comprising, a measuring light source and sensor unit positioned at an angle to the perpendicular of the surface to allow the light to be reflected to a diffuse target surface in a known position; and a processor unit, wherein the processor unit is adapted to collect and analyze data from the a measuring light source and sensor unit and classify whether the reading of the measuring light source and sensor unit is a direct reading or a reflected reading.