I found this section very interesting: > TAI is a statistical timescale which is produced at the BIPM by combining the reports from many atomic clocks around t

I found this section very interesting: > TAI is a statistical timescale which is produced at the BIPM by combining the reports from many atomic clocks around the world. Anyone who wants to find out what TAI it is now must mark the time with some local clock that contributes to TAI. Then some weeks after now when all clocks have been combined the difference between the local clock and TAI will be known. At that point it can be said what TAI it was at the moment of interest. > There are several interesting features here. First of all, before 1977 the clocks contributing to TAI were not corrected for the gravitational redshift. Because most clocks are above sea level they tick faster than TAI should tick. Through the mid-1980s there is an annual wobble due to seasonal environmental changes at some of the clock sites. In 1995 a CCTF working group deemed that the clock frequencies should be corrected for thermal radiation, and the CIPM affirmed this in 1997. The steering of TAI to the corrected frequency occurred over three years from 1995 to 1998, and the final levelling of the curve over those years indicates that the frequency of TAI is now consistent with cesium atoms at 0 Kelvin. Basically even with TAI there are all sorts of time deviations as an artifact of history.