The Invention and Development of the Kibble Balance at NPL

The Kibble Balance, now used to realise mass in the SI, was invented at NPL, in 1975, by Dr Bryan Kibble. The technique was originally used to help unify worldwide electrical measurements by measuring the Josephson constant
$K_{J}$
which led to the 1990 conventional value
$K_{J-90}$
. Subsequently it was used to measure the Planck constant leading to the redefinition of the SI kilogram in 2019. This paper describes the work carried out at NPL on this technique from 1975 to the present day.