Hi, I am puzzled by the use of the number 273 when converting from Celsius to Kelvin and vice versa. I know that Celsius scale is based on ice point and steam point, whereas Kelvin scale is based on triple point of water, which is very very close to ice point. I am a teacher and i was asked the above question by a student. My first gut impulse is that we assign numbers as a form of starting point for comparison. It is like asking why pi is 3.14. But just to set my mind at ease, are there further deeper reasons how this number 273 is chosen? Thanks all in advance.