Rankine (°R)

The Rankine scale (symbol: °R or Ra) is an absolute scale of thermodynamic temperature proposed in 1859 by Scottish engineer William John Macquorn Rankine. Like the Kelvin scale, its zero point is absolute zero, but its degree step is defined to equal one degree Fahrenheit, making one Rankine degree exactly equal to 5/9 of a kelvin. The scale has historically been used in aerospace and engineering thermodynamics systems within countries relying on English engineering units.