Time scales, their users, and leap seconds

Abstract

Numerous time scales exist to address specific user requirements. Accurate dynamical time scales (barycentric, geocentric and terrestrial) have been developed based on the theory of relativity. A family of time scales has been developed based on the rotation of the Earth that includes Universal Time (specifically UT1), which serves as the traditional astronomical basis of civil time. International Atomic Time (TAI) is also maintained as a fundamental time scale based on the output of atomic frequency standards. Coordinated Universal Time (UTC) is an atomic scale for worldwide civil timekeeping, referenced to TAI, but with epoch adjustments via so-called leap seconds to remain within one second of UT1. A review of the development of the time scales, the status of the leap-second issue, and user considerations and perspectives are discussed. A description of some more recent applications for time usage is included.

Atomic clock prediction algorithm: random pursuit strategy

“…Some statistics, such as the average absolute error or root mean square error obtained from the past data D, can characterize the capability of the predictor. In this work, the generalization capability is measured by equations ( 2) and (3).…”

“…The prediction algorithm is generally used to avoid or minimize the time and frequency jumps of time scale when a clock is added or removed from the clock ensemble [2]. For example, coordinated universal time (UTC) generated at the international bureau of weights and measures (BIPM) is a weighted average of readings from approximately 400 free-running atomic clocks distributed worldwide in time laboratories [2,3]. UTC's prediction algorithm is based on a quadratic polynomial model for each clock [4].…”

Timing errors and temporal uncertainty in clinical databases—A narrative review

“…We consider the true time and our erroneous measurement of time to be two different variables ( 53 ), and we define accuracy to be the difference between these two values (see Figure 1 ). For our purposes we adopted Coordinated Universal Time (UTC) as the underlying, yet unobserved, source of truth ( 54 – 56 ). Where possible we used a relatively accurate and precise master clock as a close approximation of UTC as described in Section 6.1.…”