second

     The term second (s) refers to the base unit of measure on the time (T) dimension. "It is defined by taking the fixed numerical value of the caesium frequency ∆νCs, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s−1."
      The day is divided in 24 hours, each hour divided in 60 minutes, each minute divided in 60 seconds. A second is 1 / (24 × 60 × 60) of the day. Historically this day was defined as the mean solar day; i.e., the average time between two successive occurrences of local apparent solar noon." ( Wikipedia ). Final: 11 Oct 2025.