When the measurement being used is ∆T, change in temperature, this is correct. Occasionally, like in the ideal gas law equation, the measurement is T, or absolute temperature, which requires zero offset. In these cases, Celsius will give the wrong answer.
As I said
It’s just usually using the one with zero offset makes the math easier
You can use Celsius in the ideal gas law. You just have to make sure to include the offset in your calculation. There is no loss of precision by using Celsius, and it isn’t wrong. It’s just the math is easier if you use kelvin, because as you point out (in this case) it’s the ratio of the absolute T that’s important, and a delta T is not enough.
By including the offset in the calculation, you have converted to kelvin.
Yes, as I said repeatedly, the math is easier which is the reason. If you didn’t include the offset in the calculations, you wouldn’t lose precision, you’d just be wrong.
I’m at a loss as to what you don’t understand.
