The DoD time reference, the U.S. Naval Observatory Master Clock, is backed up by the Alternate Master Clock pictured here at Schriever Space Force Base, Colorado, Oct. 27, 2023.  The Master Clock in Washington, D.C. and the Alternate Master Clock at Schriever SFB are both disciplined to a timescale compromised of signals from multiple atomic clocks. Most users receive this time through the Global Positioning System. (U.S. Space Force photo by Airman 1st Class Justin Todd)