e Christian calendar. None of this is at all useful when trying to agree on a universal definition of time, so in 1960, Coordinated Universal Time, or UTC, was introduced as an internationally agreed time system that uses the Western year numbering. However, even this is totally useful for a 268 Open Radio Access Network (O-RAN) Systems Architecture and Design couple of reasons. First, to keep UTC roughly in line with the rotation and orbit of the earth, it includes the concept of leap years and leap seconds. Everyone is familiar with the former, but leap seconds are less well known since they have little impact on everyday life. They are, however, used to maintain time relative to the rotation of the earth and one can be added, or removed, up to twice a year to avoid days slipping with respect to sunrise and sunset. Both leap years and leap seconds become significant when calculating the elapsed time, measured in seconds-between two events a long time apart since one must consider how many leap year days and how many leap seconds were in the period. For days added by leap years, this is merely an extra complication, since it is absolutely defined when such days are added, but for leap seconds, it becomes impossible since they are added (or removed) largely arbitrarily based on the Earth's rotational speed. Therefore it is impossible to calcu- late the number of seconds from one event to another, specified in UTC, over a long period without having additional information in the form of a list of leap seconds. To avoid this, an alternate timescale referred to as an International Atomic Time, or TAI, was introduced. TAI is very similar to UTC, except that it does not include leap seconds. This means that every time a leap second is added to a day TAI slips a further second behind UTC. As of early 2021, TAI is 37 seconds behind UTC. Fig. 8-2 shows how TAI slips from UTC. The second problem, which affects both UTC and TAI, is that the division of time into years, days, hours, minutes, and seconds, is unnecessarily com