Zeroth laws– hiding in plain sight [Basicmetrology]

The most famous and widely accepted "zeroth law" is the zeroth law of thermodynamics. The first and second laws were already in place, but a preliminary law was seen to be missing, perhaps because it was too "obvious." The missing piece postulates the existence of temperature and provides the rationale behind instruments (thermometers) that can measure temperature. It is this metrological oversight that makes this zeroth law and others like it a fit subject for a column on basic metrology.