Scientists have taken a major step toward the ambitious global goal of “redefining the second” by the end of this decade. For context, researchers say an optical clock would not gain or lose a second for billions of years. Rachel Godun coordinated a multi-institutional group of researchers who measured 38 frequency ratios simultaneously for ten different optical clocks. In total, the comparison produced 38 different frequency ratios measured simultaneously, four of them for the first time. Researchers carried out an extensive coordinated comparison of optical clocks, including this ytterbium ion optical clock at NPL.