The melting point of ice, when exposed to air of normal atmospheric composition and normal atmospheric pressure at sea level, is defined as 273.15 K or 0.000 °C on the ITS90. That is to say, the temperature of every water/ice interface is exactly 0 °C. If one crushes up the ice to make a moist slurry, no part of the mixture is very far from such a water/ice interface, so the entire slurry rapidly sets to the temperature of the interface. The surface of a contact thermometer placed into the slurry would be in close contact with a reference temperature of 0 °C, and the contact thermometer will attain that temperature with a relatively small immersion.

• What uncertainty can be claimed using the crushed ice point? 

• Depending on the claimed uncertainty, what are the minimum requirements in maintenance and use? 

• How can one use the crushed ice point best?

With metrology enabled three most common scenarios are discussed in detail below and underpinned with uncertainty budgets. The latter based on extensive use in absolute temperature scale realization.