Well stated, Bill. ---- Original message ---- >Date: Wed, 9 Jan 2008 22:52:08 -0500 >From: Bill Hooper <[EMAIL PROTECTED]> >Subject: [USMA:40022] Re: °C vs C° >To: "U.S. Metric Association" <[email protected]> > > 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 > ========================== > SImplification Begins With SI. > ==========================
