These specimens used for testing any surface finish quality have long proven their value in praxis. They serve for touch and or sight comparisions with the surface of work pieces that are produced using the same manufacturing process. Condition is that materials have to be comparable.
When comparing the workpiece surface against the specimen, roughness is not quantitatively expressed. The assessment of the extent to which the surface finish of both is alike can only be subjective.
Sight comparison requires optimum light source angle. For small surfaces, the use of a magnifying glass with up to 8x magnification is recommended.
Touch comparison is made using the finger nail or a small cooper piece like a coin, for instance.