# Time Services

The second is realised with time and frequency standards („Atomic Clocks“) at the BEV. By way of international time comparisons via GNSS-Satellites the BEV contributes to the International Atomic Time TAI and thus to the Coordinated Universal Time UTC.

The TAI arises from the definition of the second while the UTC is derived from the TAI allowing for the variation in earth rotation by approximation. The second is the SI unit, which can be realized with the lowest measurement uncertainty. Since 2019 the base unit second has a pivotal position in the SI. Six of the seven defining constants have the second in the composition of their derived units. All base units, except the mole, are traceable to the second.

Time and frequency standard