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Comment by __alexs | Hacker News Reader

If the difference between two numbers in Celsius is Kelvin, what unit is the difference between two numbers in Fahrenheit?

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Rankine.

Fahrenheit. When subtracting two quantities the result has the same unit, we just use Kelvin because it's the appropriate SI unit.

We can't use Kelvin for Fahrenheit differences though. That only works for Celsius. Kelvin is Celsius with absolute zero. Fahrenheit with absolute zero is Rankine.

The other guy who responded to the parent is right. The absolute scale for measuring the difference between two Fahrenheit degrees is Rankine.

Just for the sake of sheer pedantry. The scale for measuring the _ratio_ is Rankine. You can measure differences with an _ordinal_ scale, which is what Celsius and Fahrenheit are.

For even more pedantry, Celsius and Fahrenheit aren't just ordinal scales. They are called interval scales, which lie between ordinal and ratio scales:

> Another typical example is the Celsius scale, which is divided into 100 equal degree sections between the freezing and boiling points of water. Unlike the intervals in nominal and ordinal scales, it is possible to make calculations with individual data points in interval scales. The difference in temperature between 10°C and 20°C is the same distance as between 40°C and 50°C. In contrast to ratio scales, interval scales lack a natural zero point. In the case of the Celsius temperature scale, '0°C' is an arbitrarily chosen zero point (whereas the Kelvin temperature scale begins at the absolute zero point with 0K (-273.15°C/-459.67°F). Multiplications with an interval scale are therefore not useful. While it is true for the Kelvin ratio scale that 100K defines double the heat energy in a mass as 50K, this is not true for 50°C/100°C.

https://www.statista.com/statistics-glossary/definition/320/...

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