How Does Atomic Time Get to Your Phone?

U.S. Naval Observatory (USNO) staff in Washington, D.C., and Colorado Springs operate an ensemble of around 100 atomic clocks.

USNO sends data from its clocks to the International Bureau of Weights and Measures (BIPM) in France. Around 90 other countries also send in data.

BIPM produces a weighted average of all the data to create the time scale known as Coordinated Universal Time, or UTC.

(A time scale is an agreed-upon system for keeping time using data from clocks around the world.)

BIPM tells every contributing clock lab how far off its clocks are from UTC.

USNO timekeepers adjust their time scale, UTC(USNO), which is displayed on the USNO master clock in Washington, D.C.

On board each of the 31 GPS satellites operated by the U.S. Space Force are less accurate atomic clocks.

UTC(USNO) is sent from Schriever Space Force Base in Colorado to the GPS satellites to correct their onboard clocks.

Cellphone towers receive time signals from GPS satellites.

Your cellphone and smartwatch receive time signals from cell towers and correct their internal clocks.