°R. meaning in Measurement Unit ?

The Rankine scale () is an absolute scale of thermodynamic temperature named after the Glasgow University engineer and physicist Macquorn Rankine, who proposed it in 1859. Just like the Kelvin scale, which was first proposed in 1848, zero on the Rankine scales is absolute zero, but a temperature difference of one Rankine degree is defined as equal to one Fahrenheit degree, rather than the Celsius degree used on the kelvin scale. Thus, a temperature of 0 K (−273.15 °C; −459.67 °F) is equal to 0 °R, and a temperature of −459.67 °F is equal to 0 °R.

The Rankine scale is still used in engineering systems where heat computations are done using degrees Fahrenheit.

The symbol for degrees Rankine is °R (or °Ra if necessary to distinguish it from the Rømer and Réaumur scales). By analogy with the SI unit, the kelvin, some authors term the unit Rankine, omitting the degree symbol.

Some important temperatures relating the Rankine scale to other temperature scales are shown in the table below.