Researchers at the University of Science and Technology of China developed a strontium optical lattice clock with stability and uncertainty below 10⁻¹⁹, losing or gaining less than 1 second in 30 billion years. Optical clocks are considered the most precise timekeeping devices currently available. They measure time by using the frequency of light emitted when electrons transition between energy levels in atoms. They can directly support the redefinition of the second in the International System of Units.