Scratch visibility grades are described by a series of arbitrary numbers: 10, 20, 40, 60, 80 where the brightest scratches, the easiest to see using the naked eye, are grade 80, while the most difficult to detect are grade 10. A scratch on a tested part is compared with an industrial or military standard (master) on which there are scratches of different degrees of visibility and the comparison is made using the naked eye, under controlled lighting conditions. It is important to recognize that this is a subjective test and its results can vary between different people. The scratches' visibility largely depends on their shape, and contrary to popular belief, there is little correlation between the scratch's visibility grade and its width. One cannot measure the width of a scratch to determine its grade.