Thermodynamic temperature in degrees Rankine are converted to kelvins by "dividing" by 1.8 ("T" = "T" ÷ 1.8). Although the kelvin and Celsius scales are defined using absolute zero (0 K) and the triple point of water (273.16 K and 0.01 °C), it is impractical to use this definition at temperatures that are very different from the triple point of water. ITS-90 is then designed to represent the thermodynamic temperature as closely as possible throughout its range. Many different thermometer designs are required to cover the entire range. These include helium vapor pressure thermometers, helium gas thermometers, standard platinum resistance thermometers (known
Wedgwood scale The scale was divided into 240 equidistant parts. The unheated piece of clay would fit the 0.5-inch gap giving the zero temperature reading. After annealing, the clay cylinder would shrink and fit somewhere in between the left and right ends of the bars, and the temperature could be read from the scales on the bars. The origin (0°) on Wedgwood scale was set at the onset temperature of red heat, . The scale had 240 steps of and extended up to . Wedgwood tried to compare his scale with other scales by measuring the expansion of silver as a function