Atomic clocks take a step toward redefining the second
A new clock comparison is the most precise yet, accurate to within a quadrillionth of a percent
![a ytterbium atomic clock in a NIST lab](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2021/03/032421_EC_atomic-clock_feat.jpg?fit=1030%2C580&ssl=1)
Scientists compared three atomic clocks, including the ytterbium atomic clock shown, in a step toward a future redefinition of the second.
N. Phillips/NIST