Scale of temperature the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale two years before his death. The degree Celsius (°C) can refer to a specific temperature on the Celsius scale as well as a unit to indicate a temperature "interval "(a difference between two temperatures or an uncertainty). From 1744 until 1954, 0 °C was defined as the freezing point of water and 100 °C was defined as the boiling point of water, both at a pressure of one standard atmosphere. Although these defining correlations are commonly taught in schools today, by international agreement the unit "degree Celsius" and
Celsius same is "40°C ± 3 K", which can be commonly found in literature. Celsius measurement follows an interval system but not a ratio system; and it follows a relative scale not an absolute scale. For example, 20 °C is not twice the heat energy of 10 °C; and 0 °C is not the lowest Celsius value. Thus, degrees Celsius is a useful interval measurement but does not possess the characteristics of ratio measures like weight or distance. In science and in engineering, the Celsius scale and the Kelvin scale are often used in combination in close contexts, e.g. "a measured