IUPAC definition : SI base unit of time (symbol: s). The second is 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.;
SI base unit of time (symbol: s). The second is 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.