The standalone standard clock is zeroed with time from which source?

• A. Global Positioning System time
• B. US Naval Observatory time
• C. Local civil time
• D. International Atomic Time

Answer: (B)

Stand-alone standard clocks are set to an authoritative time reference so everyone uses the same civil time. The official source for that reference in the United States is the United States Naval Observatory time, which provides the realization of UTC used for national timekeeping. Zeroing a clock to USNO time ensures it stays in sync with civil time and properly incorporates leap seconds, so it remains consistent with other systems that rely on UTC.

Using GPS time would ignore leap seconds and drift relative to civil time; local civil time varies by location and isn’t a single global standard; International Atomic Time is a highly precise atomic scale without leap seconds, so it wouldn’t match the civil time most systems aim to reflect.