Information about Celsius
Degree Celsius is a measurement unit named after a Swedish astronomer.
Celsius used two fixed points for his temperature scale. He defined 0 degrees centigrade as the temperature where water starts to freeze. He used the boiling point of water as second fixed point and defined it as 100 degrees centigrade.
The modern definition after DIN 1345 uses the Kelvin scale as reference. 0 degrees centigrade equals 273.15K. So that the freezing and boiling point are no longer the historical value but rather 0.002519 °C and 99.9839 °C.