Reading 33, on weather derivatives... Glitch or is it just m difference, currently, studying

ishfaque

Hi!
I’m currently studying AI for PM, and just wanted to know… p 187 of the 5th volume seems to define heating degree day and cooling degree day as being the same…
“A HDD is the maximum of zero and the difference between the average daily temperature and 65 degrees Fahrenheit. A CDD is the maximum of the difference between the average daily temperature and 65 degrees Fahrenheit, and zero.”
Now… this sounds like the two are the same…
Any clue what I’m missing there? (Sorry, English is not my first language…)
Thanks