the conversion can be a function of Temperature or it can be just a percentage conversion
If the conversion is 50%, then you can directly enter the conversion to be 50 instead of the function.
If the conversion is given as a of function of temperature, then it depends on whether the term T in the function is in degree C or K. If it is in K, then it can be used as it is. If it is in C, then you need to convert the function to K by using changing T to T-273.15. Please note that you are converting the function of temperature and not the temperature value. Thats why, it has to be -273.15.