1. A method for calibrating a specular reflectance measurement sensor for use in a device, the method comprising: providing a sensor module, the sensor module comprising: (i) an illuminator configured to emit a beam of light at a target, thereby producing specular reflectance at an angle; (ii) a linear array sensor configured to detect that specular reflectance; and (iii) a processor configured to process the specular reflectance detected by the sensor; measuring a reflectance profile of a diffuse white reflecting surface using the sensor module and storing it in a memory; determining a non-uniformity correction factor which quantifies reflectance non-uniformity differences between a target and the diffuse white reflecting surface; measuring a specular reflectance profile of a target using the sensor module; determining a calibrated specular reflectance profile of the target based upon the pixel-wise non-uniformity correction factor, and providing the calibrated specular reflectance profile of the target to the device.