The Naval Observatory Alternate Master Clock, located on the 2nd Space Operations Squadron's operations center, is accurate to within one second every 20 million years. The clock showed 23:59:60 Saturday as 2nd SOPS and USNO professionals added the first leap second in seven years.

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Photo credit: © PJF Military Collection / Alamy / Afripics
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Keywords: air, airforce, force, military, states, united, usa