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Communications of the ACM


Split Second

leap second clock time

Credit: NASA

The question, "what time is it?" seems simple on its face, but it is a question that delegates to the World Radiocommunication Conference will struggle with when they meet in Geneva this November. At issue is whether to keep the world's definition of time as it is, or to alter it by removing the concept of a leap second.

On 26 occasions since 1972, clocks around the world have stopped for one second to adjust for the difference between the Earth's rotation and Coordinated Universal Time (UTC, under the French acronym). Those adjustments mean the sun remains over the Prime Meridian at noon, but they also cause a host of problems for computers worldwide. For example, the leap second that happened on June 30, 2012 crashed the software powering airline reservation systems in Australia, and also led to issues with services including Reddit, Foursquare, and Yelp.


Steve Allen

With 2 months to WRC-15 there is no obvious resolution. This week's view of the ITU is at where the presentation on Agenda Item 1.14 by Zuzek shows no consensus on the fate of leap seconds. Further insight into the international posturing can be heard in the audio of the Inter-regional Sep 3 afternoon session at

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