Discussion below the question Does the US National Weather Service use Celsius or Fahrenheit? and correction of my original use of "Centigrade" to the modern Celsius lead me here.
For example, in the merriam-webster.com's entry for centigrade it says:
Did You Know?
The centigrade scale is essentially identical to the Celsius scale, the standard scale by which temperature is measured in most of the world. Anders Celsius of Sweden first devised the centigrade scale in the early 18th century. But in his version, 100° marked the freezing point of water, and 0° its boiling point. Later users found it less confusing to reverse these two. To convert Fahrenheit degrees to centigrade, subtract 32 and multiply by 5/9. To convert centigrade to Fahrenheit, multiply by 9/5 and add 32.
seems to equivocate by using the term "essentially".
Wikipedia's page for Centigrade says:
Centigrade, a historical forerunner to the Celsius temperature scale, synonymous in modern usage
comes closer since synonymous suggests (but doesn't explicitly say) that the two are numerically identical.
If they are both linear scales, and have the same two fixed (and non-identical) points, perhaps there's a mathematical proof that they are identical?
Question: When and how did usage of the term Centigrade give way to Celsius? Are/were they in fact numerically identical?
When did "Later users (find) it less confusing to reverse these two."?