The ability to redefine the kilo in 2018 will rely on determining the Planck constant using two different methods. One method balances a kilogram weight and a force generated by the current in a coil of wire within a magnetic field and the other relies on counting atoms in a silicon sphere. Resolving small discrepancies between the different electrical balances used to generate the kilogram experimentally and remove inconsistencies between the balancing and atom counting methods were remaining problems hampering the kilograms redefinition. The EMRP project Realisation of the awaited definition of the kilogram - resolving the discrepancies has enabled the international community to pool resources and successfully get agreement between these techniques.

Over the longer-term, the atom-counting method will make the kilogram definition accessible to any laboratory capable of carrying out surface characterisations and volume measurements. Relatively inexpensive natural silicon spheres will be usable as mass transfer standards. Spheres may transform the kilograms traceability chain and significantly increase the number of labs able to experimentally achieve an SI definition of the kilogram. 

Optical technologies are important for many applications from fibre optic communication networks to earth observation and healthcare. To take advantage of LED technologies, new highly accurate measurement standards are needed to support SI traceability in radiometry – the measurement of light in any part of the electromagnetic spectrum. EMRP project New primary standards and traceability for radiometry has developed a new radiometry standard based on Predictable Quantum Efficiency Detectors (PQED) that for the first time can be easily used by calibration and testing laboratories, improving access to the candela, the SI unit of luminous intensity. The PQED provides a direct link to the fundamental constants used in the SI redefinition, therefore it does not require calibration using any other method.

Precise measurements of impedance – the resistance a circuit presents to an alternating current – is vital in modern electronics. Impedance values are currently defined using the Quantum Hall Effect, which can be scaled to create a range of impedance values depending on the number of windings in the two transformers used. Josephson Bridges, based on dual alternating current Josephson voltage standards, enable unprecedented flexibility in high-precision impedance calibrations but these take a long time to achieve stability. EMRP project Automated impedance metrology extending the quantum toolbox for electricity has developed and validated a software driven Josephson Bridge that can automatically set impedance ratios, allowing multiple ratios to be achieved rapidly with a single instrument.

Advanced analytical instruments, such as Atomic Force Microscopes and Scanning Electron Microscopes, are being used to make nanoscale dimension measurements, but their users need improved calibration standards to have confidence in the measurements made. Existing standards, based on precisely machined blocks of material to form nano-sized steps, is a time-consuming process that produces standards down to only 6 nm. EMRP project Crystalline surfaces, self assembled structures, and nano-origami as length standards in (nano)metrology successfully created silicon lattices with reproducible step height and lateral features that demonstrate the feasibility of using crystal lattices for sub-nanometre dimension measurements. Further evaluation of this new capability is needed to ensure its international acceptance and to enable this type of standard to be used in nanoscale dimension measurements.