U.S. Air Force Senior Airman Ruben Mejia, 1st Maintenance Squadron precision measurement equipment laboratory journeyman, calibrates parallel bars at Langley Air Force Base, Va., Aug. 18, 2015. Langley PMEL specialists are responsible for the accuracy and tolerance of electronic and physical dimensional test equipment across the installation. (U.S. Air Force photo by Senior Airman Kayla Newman/Released))