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2.  Coordinated Universal Time, better known by its acronym UTC, is the legal basis for timekeeping for most countries in the world, and is the de facto time-scale in most others.  UTC is defined by ITU’s Radiocommunication Sector (ITU-R).  The current standard, Recommendation ITU-R TF.460-6, entitled “Standard-frequency and time-signal emissions”, recommends the application of leap seconds to maintain UTC close to Universal Time 1 (UT1) — a time proportional to the rotation angle of the Earth on its axis. The leap second came into use in 1972. 2

3.  A number of years later, some administrations expressed concerns about the implementation of the leap second, and a study question on the future of the UTC time-scale was adopted in 2000, Question ITU-R 236/7 “The Future of the UTC Time Scale”, generated by Study Group 7 (SG7) (Science Services) Working Party 7A (WP7A) (Standard Frequency and Time Signal Services).  Question 236/7 was structured to address the future definition and use of UTC in the ITU-R recommendations, taking into consideration that any major technical change to UTC could have a potentially significant impact on communications networks, navigation systems, time/frequency distribution systems and indeed all aspects of civil/military timekeeping. 3

4.  The main issues to be addressed were what the requirements for globally-accepted time scales for use both in navigation and telecommunications systems and for civil time-keeping are, and to determine whether the current leap second procedure satisfies user needs or should an alternative procedure be developed. 4

5. The various discussions and studies that had been taking place on the question of establishing UTC as a continuous atomic time-scale led to this matter being submitted to the 2012 World Radiocommunication Conference (WRC-12) for decision. 5 Proposals have been made since 2003 to revise Recommendation ITU-R TF.460-6 in order to achieve a continuous time-scale.

6. WRC-12 noted that the sporadic insertion of leap seconds may upset systems and applications that depend on accurate timing. Some organizations involved with space activities, global navigation satellite systems, metrology, telecommunications, network synchronization and electric power distribution have requested a continuous time-scale. 6

7.  For other specialized systems and for local time-of-day, however, a time-scale reckoned with respect to the rotation of the Earth is needed. Also, a change in the reference time-scale may have operational and hence economic consequences. 7

8.  Consequently, as many WRC-12 participants felt that more information was needed before a decision could be reached, the conference adopted Resolution 653 (WRC ‑ 12), which reflected their agreement to bring the question to the attention of relevant outside organizations, to have ITU–R Working Party 7A carry out further studies, and to include the topic as an agenda item for WRC ‑ 15. 8

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10. Under Agenda item 1.14, WRC-15 will consider the feasibility of achieving a continuous reference time-scale:  Remove the leap second procedure in the definition of UTC (retain UTC name or adopt a new name);  Keep UTC as it is today and disseminate UTC and a second, continuous, time-scale on an equal basis;  Keep UTC as it is today but enable the recovery of the International Atomic Time (TAI) from the current implementation of UTC or use a continuous system time-scale. 10

11. Introduce a continuous reference time-scale and stop insertion of leap second Method A1: stop the insertion of leap seconds in UTC to be effective no less than five years after the date of entry into force of the Final Acts of the WRC-15; Method A2: similar to A1 but also change the name of UTC. METHOD A: Retain UTC as currently defined and introduce a continuous reference atomic time-scale based on TAI with an offset to be broadcasted on an equal basis. METHOD B: No change to UTC: Method C1: No change UTC definition in Rec. ITU-R TF.460- 6, UTC will remain the only time-scale that is broadcasted; Method C2: similar to C1 but also Rec. ITU-R TF.460-6 would be amended to allow using continuous system time-scales in addition. METHOD C: ALL METHODS PROPOSE SUPPRESSION OF RESOLUTION 653 (WRC-12). 11

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