The Birthday of Anders Celsius (1701)

Celsius invented the centigrade temperature scale (0° freezing, 100° boiling). The scale is linear: C = (F‑32)/1.8. The Kelvin scale (absolute) is K = C + 273.15. Temperature scales are affine transformations of the thermodynamic temperature (based on ideal gas law). Celsius originally had 0° boiling, 100° freezing – later reversed. The Celsius scale is used worldwide for everyday temperatures. Mathematics of thermometry: calibration (two fixed points), interpolation, and the zeroth law of thermodynamics. Celsius gave us a number to feel.