Parry in 1955 at NPL. Calibration of the caesium standard atomic clock was carried out by the use of the astronomical time scale ephemeris time (ET). This led to the internationally agreed definition of the latest SI second being based on atomic time. Computing Early computers NPL has undertaken computer research since the mid-1940s. From 1945, Alan Turing led the design of the Automatic Computing Engine (ACE) computer. The ACE project was overambitious and floundered, leading to Turing's departure. Donald Davies took the project over and concentrated on delivering the less ambitious Pilot ACE computer, which first worked in May 1950. Among those who worked on the project was American computer pioneer Harry Huskey. A commercial spin-off, DEUCE was manufactured by English Electric Computers and became one of the best-selling machines of the 1950s. Packet switching Beginning in the mid-1960s, Donald Davies and his team at the NPL pioneered packet switching, now the dominant basis for data communications in computer networks worldwide. Davies designed and proposed a commercial national data network based on packet switching in his 1965 Proposal for the Development of a National Communications Service for On-line Data Processing. Subsequently, the NPL team (Davies, Derek Barber, Roger Scantlebury, Peter Wilkinson, Keith Bartlett, and Brian Aldous) developed the concept into a local area network which operated from 1969 to 1986, and carried out work to analyse and simulate the performance of packet-switched networks, including datagram networks. Their research and practice influenced the ARPANET in the United States, the forerunner of the Internet, and other researchers in the UK and Europe, including Louis Pouzin. NPL sponsors a gallery, opened in 2009, about the development of packet switching and "Technology of the Internet" at The National Museum of Computing. Internetworking NPL internetworking research was led by Davies, Barber and Scantlebury, who were members of the International Networking Working Group (INWG). Connecting heterogeneous computer networks creates a "basic dilemma" since a common host protocol would require restructuring the existing networks. NPL connected with the European Informatics Network (Barber directed the project and Scantlebury led the UK technical contribution) by translating between two different host protocols; that is, using a gateway. Concurrently, the NPL connection to the Post Office Experimental Packet Switched Service used a common host protocol in both networks. NPL research confirmed establishing a common host protocol would be more reliable and efficient. The EIN protocol helped to launch the proposed