Most of you will be aware that the SI units are being redefined in terms of physical constants like Planck's and Boltzmann's and the elementary charge. We'll at last be rid of the last standard artefact, the kg, a lump of metal in a vault near Paris, France.
Central to the new definition of the kg stands the Kibble balance (Watt balance), that relates mass to voltage and current, which can me measured with great precision using interferometry, the Josephson effect and the quantum hall resistance.
One factor that enters in the determination of the new kg is the local value of g, the acceleration due to gravity. I have been unable to find a description of how that is done. The issue is totally glossed over in the publications I've looked through. It's done away with merely by saying that it's measured using an accurate absolute gravimeter.
Right.
Does anyone know how this is done? Surely that instrument must be pretty sophisticated itself?
Jeroen Belleman