Each artefacts are in comparison in vacuum and in air. By comparing The 2 artefacts of identical nominal fat, the massive quantity variation demonstrates the air buoyancy and therefore leads to a very precise resolve of air density. The buoyancy artefacts are predominantly used for the M_one vacuum mass comparator. https://bailing-wire13455.wizzardsblog.com/31071234/getting-my-bailing-wire-to-work