How does Maple 14 convert Fahrenheit to Celcius

using
convert(32, temperature, Fahrenheit, Celsius)

I get 0, the known开发者_JS百科 freezing point of water in Celsius

using
convert(32, units, Fahrenheit, Celsius)

I get 160/9 approx. 17.778 Celcius

How does Maple get this answer 160/9

I tried this as well...

using
convert(100, temperature, Celsius, Fahrenheit)

I get 212

using
convert(100, units, Celsius, Fahrenheit)

I get 180

This is a "relative" versus "absolute" issue.

In absolute terms, 1 deg C is 33.8 deg F. That's on an absolute scale.

In other words, 1 deg C above the freezing point of water is the same temperature as 1.8 deg F above the freezing point of water. It's an absolute scale; eg. the fixed freezing point where they match at 0 deg C = 32 deg F.

And that leads to the well known relative scale, 1 deg C = 9/5 def F. That means that for every 1 deg C of increase, there is a 9/5 deg F increase. This is a relative scale; there's no fixed reference such as freezing or boiling points.

convert/temperature does the absolute scale temperature conversion.

convert/units does the relative scale "temperature increment" conversion.

Suppose I say to you, what's 10 deg C in Fahrenheit? In your head you might do it like so: Divide by 5 to get 2, multiply by 9 to get 18, and add 32 to get a final result of 50 deg F. You added the 32 deg F at the end, because this was an (absolute scale) temperature question. Now what if I subsequently asked a second question: what's 11 deg C in Fahrenheit? That's 1 deg C more than before. How many deg F do you need to add to the previous answer? It's certainly not 33.8 deg F more that you'd add to the earlier answer. No, you'll just take 1 deg C = 1.8 deg F, since this is an increment. And you'll get 50 deg F + 1.8 deg F = 51.8 deg F. That was a relative increment over the first answer.