Hail Ants I honestly can’t see how F is superior (or inferior) to C for measuring weather. Your statement that:
is the whole story. Substitute your 50s 60s 70s 80s etc for “low teens, high teens, early 20s, late 20s, early 30s” and you achieve the same outcome, a quick classification from cool to warm. Everyone who uses C knows that 0 is pretty cold and you can expect to see ice on the roads, and that 50 is hot and you’d be lucky to see ice in your freezer :).
Yes, it is pretty much the whole story.
But it always seems that suggesting switching from F to C is considered progressive and sensible, while suggesting the other is considered outright madness!
Either one you use, once you are use to it there is no advantage to switching to the other. But if a continent popped up in the Pacific and you formed a new country, when the American & French ambassadors showed up, one pushing for Fahrenheit and the other Centigrade, I’d send Pierre St. Croisant packing! 
Celsius has clear and undeniable benefits. It is easier to remember the freezing and boiling point of water at sea level.
For biologists, meteorologists, and farmers, Celsius makes much more sense. 0° C indicates a point of great significance in ecology, climate, and agriculture; 0° F indicates a point of no particular importance at all.
I think the innateness is really the only arguement. I don’t try to understand the logic of a 32 degree freezing point any more than I do 5000-odd foot mile (and yes, I know the units in between, but I’m trying to prove a point). I know that where I live I can expect temperatures from about -30 to 30 C from winter to summer, and if it’s extreme (like it was this summer and last winter) perhaps even -40 to 40 C.
It’s amazing that with so many replies, none of you have managed to answer the question in the original post. The correct answer is:
On the Centigrade scale, 100 is based on the boiling point of water.
On the Celsius scale, 100 is based on the triple point of water.
The triple point of water is 273.16 K or .01 C.
Phil Saoud correctly pointed out that no-one had yet answered the OP. Phil’s attemped answer, was, well…
The answer to the OP can be found here
As someone who operated a temperature metrology lab at a Department of Energy facility, I’d like to add my two cents.
Yes, the Celsius scale was at one time based on “0 °C = freezing point of water” and “100 °C = boiling point water”. But this is not longer the case.
The freezing and boiling points of water are no longer used to define any temperature scale. They were thrown out a long time ago for a variety of technical reasons. Instead there are exactly two temperatures which are absolutely defined: absolute zero (0 K) and the triple point of water (273.16 K). All other temperatures, including the freezing and boiling points of water, are simply known to a high degree of accuracy. As an example, the freezing point of water is not exactly 0 °C; it is a few micro-Kelvin below this value. As technology improves, we are able to determine the temperature of the freezing point of water with more and more precision.
While a very interesting discussion - no one has addressed my question yet. My question is about word usage, not Kelvin, Fahrenheit or the conversion between. I reiterate - why do older people use Centigrade and younger people use Celsius? Was a formal proclamation made by the estate of Lord Celsius?
The change in terminology was made in 1948, by the General Conference on Weights and Measures (Conférence Générale des Poids et Mesures, CGPM), which is held every four years:
“The CIPM” refers to the International Committee for Weights and Measures (Comité International des Poids et Mesures), which proposed the changes adopted by the CGPM.
It took some time for the new convention to spread. As an old fart myself, I recall that it was common to refer to “degrees centigrade” when I was in high school in the 1960s (although I learned they were also called Celsius). In college, where science classes were a bit more rigorous, it was always Celsius.
What on Earth is the triple point of water?
It’s the point at which all three phases (solid, liquid, gas) are capable of existing in equilibrium.
More specifically, it’s a temperature and pressure. For water it’s 273.16 K at 611.2 Pa, 32.288 F at 0.0060 atmospheres. You can see a diagram, the triple point is where the three lines meet ©. You can also see that at 1 atm, the liquid/ice equilibrium is near 0 C, and the liquid/vapor is near 100 C.
Hey, neat! I was unaware that there was any combination of temperature and pressure at which water could exist in three phases simultaneously.
Looking at that graph, though, what the hell is Ice III?
Hey, neat! I was unaware that there was any combination of temperature and pressure at which water could exist in three phases simultaneously.
Looking at that graph, though, what the hell is Ice III?
"Ice 3!! You thought regular ice was solid… but you were wrong! Get ready for…
Ice III
Ice III… the pressure’s on!
There are more state changes than just solid, liquid, gas. You can also get things like changes in the crystalline structure of a solid, for instance. All of the ices are solids, but they have different crystalline structures. What this means is that if you vary the temperature and pressure of ice and cross that line, all of a sudden properties like the density of the ice will change abruptly with a small change in temperature.
Thanks to Desmostylus and Colibri, in particular, for settling this issue. My memory of high school chemistry has obviously tarnished with age. At least I can take solace in the fact that I was able to hover near the answer. The discussion of which scale is superior was killing me.
Here it is so hot that people back home in the Cold World get confused whether I am actually talking centigrade/celsius or fahrenheit.
