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Warmness is illustrated by this icon for warm or cool sensations.

Any mild perception of heat that happens in routine human activity is called a safe thermal sensation. Safe thermal sensations are described using words like warm, cool, balmy, chilly and lukewarm. They are similar to the temperature of a living person. The reference experience for these sensations is touching steam. So to make a binary description of a safe thermal sensation, compare it to touching steam. 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 safe thermal sensation and express this as \delta_{\tau}=0. If the sensation is like touching steam, then say that it is warm. Express this as \delta_{\tau}=+1. If the sensation is not like touching steam, then say that it is cool and that \delta_{\tau}=-1. The number \delta_{\tau} is called the warmness. These relations are mathematically expressed by

\delta_{\tau} \equiv \begin{cases} +1 &{\text{if a thermal sensation is warm }} \\ \; \; 0 &{\text{if a sensation is not safe}} \\ -1 &{\text{if a thermal sensation is cool }} \end{cases}

Reference Constant for Warmness

The numerical constant associated with the thermal sensation of touching steam is called the boiling point of water. It is symbolized by T_{\mathsf{boil}}. For ordinary terrestrial conditions near sea-level, it has a value of T_{\mathsf{boil}} = 100 \     \left(   {\degree} \mathsf{\textsf{C}}  \right) For more about how this number is used, please see the discussion of laboratory experiments and the temperature of charmed quarks.