Thanks, John. So, in rough orders of magnitude… how many times worse are our problems of transferability than theirs? Jonathan On 17 Nov 2018, at 09:53, John <[log in to unmask]<mailto:[log in to unmask]>> wrote: Just in case list members may have not noticed this. The redefinition of the SI units is now upon us. On 16th November 2018, measurement scientists from more than 60 countries have come together to witness the vote on the redefinition of the International System of Units (SI), changing the world's definition of the kilogram, the ampere, the kelvin and the mole. The biggest issue was that, the base unit kilogram is based on an artifact, a platinum-iridium cylinder (the international prototype kilogram, IPK) manufactured in 1879 and stored at the BIPM. There is an intrinsic uncertainty in the long-term stability of the IPK. In principle, this instability also impacts other SI units that depend on the kilogram, among which is the mole. The redefinition links the unit of mass to fundamental or atomic constants. In practice, nothing will really change, but in an ISO dominated scientific world, where the provenance/traceability of every measurement matters, this is of some relevance. Nice Utube video explaining the makeover from the BIPM https://www.bipm.org/en/about-us/ Introduction to the new definition of the mol that does not rely on the mass of a kilogram found here from IUPAC https://iupac.org/new-definition-mole-arrived/ The paper describing the new definition in some detail here https://www.degruyter.com/view/j/pac.2018.90.issue-1/pac-2017-0106/pac-2017-0106.xml FAQ’s from the BIPM here https://www.bipm.org/utils/en/pdf/SI_FAQs_EN.pdf As far as temperature is concerned The new definition of the kelvin has no immediate impact on the status of the widely-used ITS-90 and PLTS-2000 temperature scales. So traceability back to reference thermometers should not be a problem, this is covered in the FAQ link above ------ACB discussion List Information-------- This is an open discussion list for the academic and clinical community working in clinical biochemistry. Please note, archived messages are public and can be viewed via the internet. Views expressed are those of the individual who posts and they are solely responsible for all message content. The ACB does not monitor posts. ACB Web Site http://www.acb.org.uk Green Laboratories Work http://www.laboratorymedicine.nhs.uk List Archives http://www.jiscmail.ac.uk/lists/ACB-CLIN-CHEM-GEN.html List Instructions (How to leave etc.) http://www.jiscmail.ac.uk/