Chasing the ohm

Nature Electronics, Published online: 30 April 2026; doi:10.1038/s41928-026-01614-3 The ohm has been the unit of electric resistance for more than 150 years, but what we exactly mean by ‘a resistance of x ohm’ has evolved in terms of both meaning and magnitude during that time. Its realization has changed from mercury columns to mechanical constructs, and is now linked to immutable constants and embodied in the quantum Hall effect.