With BIPM and other NMIs currently focusing on the digitalisation of the international system of units - the 'SI', the research proposed an XML schema, which, together with online access to a database of frequencies and specifications hosted by the BIPM, could allow users to obtain digital, machine-readable data, to assure the automated, correct operation of the lasers. Key extracts from the data can then be included in digital calibration certificates to demonstrate to accreditation bodies that laser-based measuring systems that are calibrated using these lasers, are truly, and digitally, traceable to the SI.

The transition to digitalise the SI will ensure that it remains robust into the future, ready to accommodate future advances in science and technology as well as reducing the burden of having to send, receive, and process all of the calibration certificates which are currently in analogue (paper) format.

NPL is building updated metre realisation lasers which incorporate digital control using a microcomputer which will be able to automatically link to the BIPM server and download the digital metre realisation data during calibration of a customer's laser. Moreover, the approach proposed in the article could be extended to other SI units, bringing similar efficiencies to their use.

Principal Research Scientist Andrew Lewis said: "For too long, this highly critical and very detailed information, used by all the national laboratories to realise the metre, has only been available in analogue format which has needed a human to interpret and to correctly transcribe every time it is updated. Now this is to be digitalised; it will lead to fewer mistakes, more automated operation, and have the benefit of providing a digital focus at the top of the digital traceability chain."