A method of assessing percentage dot in flexographic printing plates or the like includes superimposing the printing plate and a further, smooth surfaced sheet or plate of material of a reflective index greater than air, so that the "high" regions of the printing surface of the printing plate make intimate contact with the adjoining surface of said further plate. The superimposed sheet is illuminated in such a way that the difference in the light reflection between the areas of the further sheet which are not in intimate contact with the printing plate and those areas which are provide a significant difference in apparent brightness between the "high" regions and the "low" regions. The difference in apparent brightness can be detected by visual, automatic or photo detection means.