On 2008 Jan 9 , at 12:29 PM, Pierre Abbat wrote:
Was C° official, and when was it in use?
The symbol C° for Celsius temperature differences (as opposed to °C,
for the actual temperatures) never was official, as far as I know, but
I have seen it recommended several times. There is some justification
for it because temperature is the ONLY thing for which the metric
measures and the non-metric measures do not have the same zero point.
Therefore, when converting 20 °C to degrees Fahrenheit, for example,
it depends whether that 20°C figure was a specific temperature on the
Celsius scale or whether it was a difference between two temperatures
on the Celsius scale.
For temperatures we write:
T(°F) = 9/5 x T(°C) + 32
whereas for temperature differences we write (using the Greek capital
delta symbol for "difference"):
delta-T(F°) = 9/5 x delta-T(C°)
Of course, you and I can argue that, surely, anyone faced with that
kind of a question should be thoroughly familiar with what is being
measured. We should not be making conversion of values for which we
have no understanding. (If you don't know that acres measures area and
think it measures distance -- something I have found some people do
think -- then you have no business converting it into either metres or
square metres.
If you don't know whether you are talking about temperatures or about
temperature differences, you have no business converting anything (or,
for that matter, no business talking about it at all). If you DO know
what you're talking about, it would be clear and obvious, from the
context, when (and why) you need to add an extra 32.
But, none-the-less, some people find it convenient to distinguish
temperatures from temperature differences by modifying the Celsius
degree description slightly. There is no real harm done if they do it
that way, but I hope no one will let them insist that it is officially
correct or even necessary.
Bill Hooper
1810 mm tall
Fernandina Beach, Florida, USA
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SImplification Begins With SI.
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