NPL developed the first accurate caesium atomic clock in 1955, which led to the internationally agreed definition of the second being based on atomic time. Following a trip to America to see early versions of atomic clocks, NPL’s Louis Essen designed and built one that delivered much greater accuracy and stability based on the transition of the caesium-133 atom. Successive developments of this have remained the fundamental standard up to the present day.
Today, NPL operates the national time scale UTC(NPL) and the UK primary frequency standards, and uses these to contribute to global timekeeping. We also disseminate accurate time and frequency to users across the UK, via services such as the MSF radio time signal, our internet time service and NPLTime®. Atomic timekeeping underpins technologies that are part of our daily lives, such as mobile phones, the internet and global navigation satellite systems.
NPL provides customers and partners with access to trusted and reliable time, and pushes the boundaries of timing technologies.
Discover more about NPL's work on Time and frequency
Discover more about SI units