In Fahrenheit, 100 was supposed to represent human body temperature, and 0 the freezing point of brine. The problem was, the instruments of the era were too imprecise to hit those numbers square on, and the system drifted over time.
That's not the way I learned it. Zero Fahrenheit was the coldest winter day of the year wherein the thermometer was invented and one hundred was the hottest day observed that same year. It makes no difference as 32 is still the temperature of an ice/water mixture and 212 is the boiling point of water at sea level. These two calibration points correspond to zero and 100 degrees Celsius. It may seem trivial but there are only 100 degrees between the two calibration points on the metric scale and 180 on the Fahrenheit scale. It don't mean much but it all means something...
Regards,
GtG