Live Science reports.When the Universal Coordinated Time (UTC), the official international timekeeping method, don't quite sync up by more than 0.4 seconds, our clocks require an adjustment in the form of a "leap second."The last time an adjustment was needed was on New Year's Eve 2016 as a second was added at 23 hours, 59 minutes and 59 seconds.
According to the National Institute of Standards and Technology, scientists have added a leap second about every 18 months on average since 1972.
Read more on dailystar.co.uk