B Why degree rankine?

I think it should as well be °K because the degree basically refers to the step size which matters a lot. However, it simply doesn't make a difference. Most likely it's for historical reasons (which I don't know).

 

Yes, but I still think (meant as an opinion, not as an assumption) °K would be more accurate.

Yes! And I've read about many other scales I've never heard of before, too. I always thought Kelvin, Celsius, Fahrenheit and Réaumur were all.

And I learned that Celsius was an upside down scale in its beginning, i.e. freezing at 100°C, evaporation at 0°C! It has been changed by Linné shortly after Celsius' death. And the Russian also used a turned scale in the 19th century: °D (Delisle).

And I learned that the triple point of water defines Kelvin. I've always wondered where the discrepancy between 273,15°C and 273,16°C comes from. I mistakenly thought it had something to do with the change of definition since my school days.