Optical metrology is providing more information, faster, about surfaces that were once impossible to measure and understand. When an engineer includes a surface finish specification on a print, the intent is usually not just for aesthetics. Surface finish affects how a part will fit, wear, reflect light, transmit heat, distribute lubrication and accept coatings. The finish should be determined by the part’s function: A surface should fulfill the engineering requirements of the application without wasting time and effort on a higher quality finish than necessary. In fact, many applications do better with a certain amount of “texture,” and too fine of a finish can be just as bad as too coarse of a finish. In the 1940s, the surface finish measurement upgraded from visually comparing patch reference standards to moving a fine stylus across a part’s surface via a transducer and amplifier. This provided part measurement data that could be recorded and analyzed against various surface parameters to evaluate its roughness, profile and waviness. For the next half century, this technique was invaluable to various industries: It helped engines last longer, improved fuel e...