Why does subtraction of two units.degC quantities give a units.delta_degC result but subtracting two units.kelvin gives a units.kelvin result in metpy

Question

I'm a metpy user.

I was calculating the unit of temperature using metpy.

I found one difference in the process of subtraction.

For Celsius and Fahrenheit temperatures, subtracting or adding values will output delta_degree_celsius, but for kelvin temperature, it will be output as kelvin.

I wonder what are the differences between these and the results.

d1 = 10 * units.degC
d2 = 5 * units.degC

d1 - d2
= 5 delta_degree_celsius

d3 = 10 * units.kelvin
d4 = 5 * units.kelvin

d3 - d4
= 5 kelvin

Because Celsius is not an absolute unit. https://unidata.github.io/MetPy/latest/tutorials/unit_tutorial.html#temperature Sure, 5 deltaDegC is e same as 5 Kelvin, but I suppose they want to remember that it came from Celsius for some reason — Pranav Hosangadi, Jan 11 '23 at 17:05

score 0 · Answer 1 · answered Jan 18 '23 at 22:29

While Kelvin and delta_degree_Celsius are equivalent, the delta_degree_Celsius is created by Pint (the unit library used by MetPy) as part of its machinery to generically handle units that have a non-0 offset. For more information, see Pint's documentation on temperature conversion.

Why does subtraction of two units.degC quantities give a units.delta_degC result but subtracting two units.kelvin gives a units.kelvin result in metpy

1 Answers1