Most accurate clock

As the SI definition of the second is based on the caesium atom, only caesium clocks can contend to be the most accurate. However a technique using an experimental strontium atomic clock by researchers at JILA, a joint institute run by the University of Colorado and the National Institute for Standards and Technology (USA), has created the most precise strontium atomic clock to date. The JILA clock will neither gain nor lose a second in around 4.5 billion years. The research was announced on 22 January 2014.