Attachment 4 Co-ordinated Universal Time

Co-ordinated Universal Time (UTC) has now replaced Greenwich Mean Time (GMT) as the accepted international standard for clock time.

It is the basis for civil time in many States and is also the time used in the world-wide time signal broadcasts used in aviation. The use of UTC is recommended by such bodies as the General Conference on Weights and Measures (CGPM), the International Radio Consultative Committee (CCIR) and the World Administration Radio Conference (WARC).

The basis for all clock time is the time of apparent rotation of the sun. This is, however, avariable quantity which depends, among other things, on where it is measured on earth. A mean value of this time, based upon measurements in a number of places on the earth, is known as Universal Time. A different time scale, based upon the definition of the second, is known as International Atomic Time (TAI). A combination of these two scales results in Co-ordinated Universal Time. This consists of TAI adjusted as necessary by the use of leap seconds to obtain a close approximation (always within 0.5 seconds) of Universal Time.