Datasheet DM006, titled “Measuring Diamond Turned Aspheric and Diffractive Surfaces,” has been released by Precision-Optical Engineering. Downloadable from the company Web site, the publication describes contact measurement systems, including the commonly used surface profiling method and the linear voltage displacement transducer technique, which uses an “on machine” probe to measure the surface form of an aspheric lens surface while mounted on the diamond turning lathe. It also discusses noncontact systems, such as measuring diffractive steps and the interferometric use of null lenses and computer-generated holograms to measure surfaces.