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Coldness is illustrated by this icon for burning or freezing sensations.

Any hazardous perceptions of heat or cold are called dangerous thermal sensations. We use words like icy, boiling, freezing, scorching, frosty and blistering to describe these sensations. They are not like touching a living person, temperatures are significantly higher or lower. The reference experience for these sensations is touching ice. So to make a binary description of a dangerous thermal sensation, compare it to touching ice. Report the result using one of the following algebraic statements. If the two experiences are not comparable, then say that the sensation is not a dangerous thermal sensation and express this by writing \delta_{T}=0. If the sensation is like touching ice, then say that it is freezing. Express this as \delta_{T}=+1. If the sensation is not like touching ice, then say that it is burning and that \delta_{T}=-1. The number \delta_{T} is called the coldness. These relations are mathematically expressed by

\delta_{T} \equiv \begin{cases} +1 &{\text{if a thermal sensation is freezing }} \\ \; \; 0 &{\text{if a   sensation is not dangerous}} \\ -1 &{\text{if a thermal sensation is burning }} \end{cases}

Reference Constant for Coldness

The numerical constant associated with the thermal sensation of touching ice is called the melting point of ice. It is symbolized by T_{\mathsf{melt}}. For ordinary terrestrial conditions near sea-level, it has a value of T_{\mathsf{melt}} = 0 \     \left(   {\degree} \mathsf{\textsf{C}}  \right) For more about how this number is used, please see the discussion of calibration and the temperature of bottom quarks.