9f7dbe57__units___UK_Metric_Association_SI_base_units_it_measures_and_its_definition
[Unit name] second [Symbol] s
Time It is the familiar unit of time that we count with our watches and clocks. It is now defined by the natural beats of a highly stable caesium atomic clock. The duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.
Base units | UK Metric Association
What it measures and its definition