On 1st January 1990 small but significant changes were made to the UK's electrical standards to bring them more closely into line with the ideal definitions of the International System of Units (SI). Similar changes were made simultaneously by other countries resulting in much improved harmonisation of electrical measurements worldwide. Although the major impact of such changes will be felt by those making high-accuracy measurements, it behoves all users of electrical measuring instruments to be aware of the situation and to consider whether any action is required on their part.