Rankine (°R)
The Rankine scale, symbol °R, was developed in 1859 by the Scottish engineer William John Macquorn Rankine. Consistently, like Kelvin, it starts at absolute zero but uses Fahrenheit-sized degrees instead of Celsius. This makes Rankine particularly useful in engineering fields within the United States, especially in thermodynamics, aerospace, and combustion studies. One Rankine equals 1°F increment, with 0°R corresponding to absolute zero. Although less common in everyday life, the Rankine scale remains important in theoretical and applied engineering, where calculations are based on the Fahrenheit system.
Fahrenheit (°F)
The Fahrenheit scale, denoted as °F, was established in 1724 by Daniel Gabriel Fahrenheit, a physicist of Polish-German origin. Initially, he based 0°F on the freezing point of a saltwater mixture and set 96°F near average human body temperature. The system was later revised so that pure water freezes at 32°F and boils at 212°F under standard atmospheric conditions. Fahrenheit continues to be the primary temperature scale for everyday purposes in the United States and some Caribbean regions, especially for weather, cooking, and household measurements. While most countries have shifted to Celsius, Fahrenheit remains popular in the U.S. due to tradition and its compatibility with customary units.