We all know how to measure things, Kilograms, Metres, Amperes, etc. because all have been defined by scientists. They are known as the SI Units, "Système International" Units, and agreed by all nations. However, some problems have been found leading to their redefinition, becoming effective this year.
John Turland will explain how the International System of Units works and why scientists are planning subtle but profound changes in the definitions of four of these units.
