Instrument 08 / a defined second
Atomic Clock
9 192 631 770 periods
of the specified cesium-133 transition define one SI second
UTC display
Device local
Session elapsed0.000 s
This page reads your device clock. It is not an atomic clock or an official source of UTC.
Why this clock exists
Since 1967, the SI second has been tied to 9,192,631,770 periods of radiation associated with a specified transition in cesium-133. The definition replaced reliance on Earth's uneven rotation with a reproducible atomic property. This luminous chamber is only a diagram; the readings still come from your device. Its honesty matters because a precise-looking display is not the same thing as a realized standard.
BIPM realization of the second