Abstract
Abstract
This contribution discusses the direct relationship of any SI unit to the defining constants. For many of the SI derived units the relationships to the defining constants are simpler than to the SI base units. Furthermore, some of the relationships directly reflect the fundamental quantum-physical effects that are exploited in the primary realisation of units. It is not the intention of this article to question the status of the seven SI base units and the distinction between the SI base units and the SI derived units, which have evolved historically and persist for pedagogical reasons, but instead to provide an alternative view of the SI. This alternative view also allows a broader and more modern presentation of metrology in general and demonstrates that, in respect of the ability to be directly realised from the defining constants, there is little practical difference between the SI base units and SI derived units.