The colourimetry is measured with a special device. This device displays colour numbers that can be assigned to a unique colour. The measurement can be carried out using two classes of instrument with different measuring arrangements. The 45°/0° geometry uses 45° circumferential illumination and a 0° view perpendicular to the same plane, which takes the surface structure into account. In the d/8° geometry, the sample is illuminated diffusely by means of an Ulbricht sphere.