A new record-breaking atomic clock is so precise it neither loses nor gains a second in five billion years - longer than the age of the Earth.
The "strontium lattice clock" is 50% more accurate than the previous record holder, the National Institute of Standards and Technology (NIST) quantum logic clock.
It is also incredibly stable, in that each tick matches the duration of every other.
Atomic clocks operate by means of atoms oscillating between two energy levels.
In the strontium lattice clock, a few thousand atoms of strontium are held in a column of laser optical traps.
Scientists detect the clock's "ticks" - 430 trillion of them a second - by bathing the atoms in very stable red laser light. The precise frequency of the laser trigger prompts the switch between energy levels.
The clock, described in the journal Nature, was developed in the US at the Joint Institute for Laboratory Astrophysics (JILA), by a team from NIST and the University of Colorado.
Group leader Dr Jun Ye said: "We already have plans to push the performance even more. So in this sense, even this new Nature paper represents only a 'mid-term' report. You can expect more new breakthroughs in our clocks in the next five to 10 years."
In terms of stability, the new clock equals the performance of NIST's world-leading ytterbium atomic clock.