Airman First Class Kourtnie Melendez, a calibration technician with the 60th Maintenance Squadron's Precision Measurement Equipment Laboratory, uses a stainless steel gauge block to measure a micrometer Oct. 25, 2011, at Travis Air Force Base, Calif., while Staff Sgt. John Cox, a quality assurance evaluator, observes her work. PMEL fine tunes countless pieces of equipment, like this micrometer that is used by a jet engine shop belonging to the California Air National Guard. (U.S. Air Force Photo/Ken Wright)