Gregory Larson, 28th Maintenance Squadron precision measurement equipment lab quality assurance inspector, demonstrates how the flatness of a measuring surface is verified using a precision optical flat and monochromatic light source at Ellsworth Air Force Base, S.D., Feb. 20, 2013. Measurements must be accurate to ensure optimal performance and prevent safety hazards. (U.S. Air Force photo by Airman 1st Class Anania Tekurio/Released)