ELLSWORTH AIR FORCE BASE, S.D. – Staff Sgt. Nicholas Tester, 28th Maintenance Squadron aerospace propulsion journeyman, operates a B-1B Lancer General Electric F-101 turbofan engine, Oct. 6. Sergeant Tester uses a variety of digital and analog gauges to measure everything from oil pressure and fuel flow to thrust and exhaust gas temperature. (U.S. Air Force photo/Senior Airman Corey Hook)