How does a  'leap second' work?
Media playback is unsupported on your device
Video

How does a 'leap second' work?

An extra second will be added to the world's clocks on New Year's Eve in order to stay in sync with the Earth's rotation. Rebecca Morelle reports.

This video has been optimised for mobile viewing on the BBC News app. The BBC News app is available from the Apple App Store for iPhone and Google Play Store for Android.

  • 31 Dec 2016