In Canada, the National Research Council is the federal agency responsible for official time. Metrologists in the Frequency & Time Group at the Institute for National Measurement Standards work to satisfy the requirements for time at all levels of precision.
The demands of science have pushed the capabilities for accurate time and frequency determination to very high levels that may appear excessively high for everyday applications. However, these capabilities provide an economical basis for many modern systems of navigation and communication, for international acceptance of Canadian measurements that satisfy traceability of ISO 9000 series of quality standards, and for measurements in diverse fields such as radio astronomy, spectroscopy, geodesy, length measurement, voltage measurement, broadcasting and much electronics manufacturing and testing.
There are also the more obvious requirements for time coordination: in radio and television networks, in automated data recording systems and in computer-controlled systems and networks. Quite apart from technical interests, part of the general public now demands time-of-day service accurate to the second for their quartz watches and clocks.
Irrespective of the precision of the time obtained, NRC time is referred to its primary cesium atomic clocks — designed, built, and maintained at the NRC time standards laboratory in Ottawa. These clocks are accurate to a few millionths of a second per year and time difference measurements with a precision of a few nanoseconds are routinely made between these clocks and a number of signals derived from secondary clocks and from radio transmissions received at the laboratory.
The NRC clocks are used in conjunction with atomic clocks in the time laboratories of other countries to construct the internationally accepted scale of time, UTC (Coordinated Universal Time), which is now the reference for the official time used by all countries. UTC is the modern implementation of Greenwich mean time, incorporating the unequalled stability of atomic clocks. UTC is kept within a second of the time kept by the vastly more irregular rotation of the Earth by the use of a leap second, if required, at 00:00 UTC January 1 or July 1.
Coordinated Universal Time is the reference time scale derived from the Temps Atomique International (TAI) calculated by the Bureau International des Poids et Mesures (BIPM) using a worldwide network of atomic clocks. UTC differs from TAI by an integer number of seconds. UT1 is the time scale based on the observation of the Earth's rotation. The various irregular fluctuations progressively detected in the rotation rate of the Earth led in 1972 to the replacement of UT1 as the reference time scale. However, it was desired by the scientific community to maintain the difference UT1-UTC smaller than 0.9 second to ensure agreement between the physical and astronomical time scales, by the introduction of leap seconds. The value DUT1 is the predicted difference UT1-UTC. It has a resolution of 0.1 second. The decision to introduce a leap second in UTC and to adjust the value of DUT1 are the responsibility of the International Earth Rotation Service (IERS). (See also leap second.)
NRC will publish the value of DUT1, UTC-TAI and upcoming leap seconds, as soon as the predicted values are reported to us by the International Earth Rotation Service (IERS). Refer to BULLETIN TF-B for the lastest report. These values are also available in the code transmitted by radio station detailed code.
As a major contributor in the development of atomic clocks, NRC has played a significant role in the regulation of UTC through international organizations since well before the present implementation of UTC in 1972.