Thanks, Bill, for the clarification. Can you point me to the BIPM documentation about avoiding using prefixes with liters?
On Sunday 16 May 2004 20:34, Bill Hooper wrote: > John Ward, > > I don't believe anything I wrote earlier contradicted what you wrote > below. Specifically I do not believe I said that the litre is > deprecated for non-precision use. I said that I understood it to be > advisable not to use the SI prefixes with litre; for example, since > 1000 L = 1 m^3, therefore the cubic metre should be used, not the > kilolitre. > > It is true that when coherent units are needed for calculations, the > litre cannot be used and any litre values must be converted to cubic > metres. But I did not intend that to mean the litre should not be used > at all. It is just the litre with SI prefixes that should be avoided, > whether coherence is a consideration or not.I said that there are good > reasons to use the litre, in agreement with your statement below. > > If you thought that something I wrote was not in agreement with your > thoughts on the matter, please tell me what it was so I may correct > myself. > > Regards, > Bill Hooper > > On 2004 May 16 , at 11:11 PM, J. Ward wrote: > > Let's examine more closely the BIPM recommendation regarding liters. > > > > The problem in 1961 was that the new definition of the liter (a cubic > > decimeter) differs from the 1901 definition by 28 parts per million. > > Therefore, for high precision measurements made in the early 1960s > > there was > > the chance of confusion in terms of whether the measurement was based > > on the > > new definition or the old definition of liter. As a result, the 12th > > CGPM > > "recommends that the name litre should not be employed to give the > > results of > > high-accuracy volume measurements." > > > > This statement does not imply that the use of liters be deprecated for > > non-precision use. Now, 44 years later, the definition of liters is > > unambiguous and the 28 ppm confusion is purely historical. > > > > On the other hand, there are good reasons to use liters. For example, > > using > > liters keeps prefixes simple and convenient. We teach people that > > milli is > > 1/1000. A liter is 1000 ml. Simple! However, a cubic meter is 1 000 > > 000 > > 000 times larger than a cubic millimeter. Furthermore, it is > > inconvenient to > > use prefixes when when they are spread out a factor of 1 000 000 000 > > apart! > > Take for example, a cubic micrometer and a cubic millimeter. "Liter" > > sure > > rolls off the tongue better than "cubic decimeter." Finally, nearly > > the > > whole world uses and understands liters for volume measurement, at > > least for > > voluments smaller than a meter cubed. > > > > John > > > > On Saturday 15 May 2004 12:48, Bill Hooper wrote: > >> On 2004 May 15 , at 2:09 AM, Pat Naughtin wrote: > >>> Keep in mind that Australia chose the simple conversion table: > >>> > >>> 1000 millilitres = 1 litre > >>> 1000 litres = 1 kilolitre > >>> 1000 kilolitres = 1 megalitre > >>> > >>> for measuring volume and capacity. > >> > >> Interesting! But BIPM recommends not using kilolitres or megalitres > >> (or > >> even millilitres). The litre is just a special name for the cubic > >> decimetre (according to BIPM) and its common multiples already have > >> other names which conform better to SI organization. > >> > >> 1 kilolitre = 1 cubic metre > >> 1 millilitre = 1 cubic centimetre > >> > >> (Admittedly, 1 megalitre is not just one cubic SI length unit, but it > >> is just 1000 cubic metres. And the cubic metre is the basic and > >> coherent SI volume unit.) > >> > >> But the main reason to avoid the litre and it's multiples is that the > >> litre is not coherent with the other SI units. (I discussed the > >> importance of coherence in another email some time ago.) > >> > >> I think it is unfortunate that Australia promotes non-SI units like > >> the > >> kilolitre and megalitre. Everything else in Australia metrication > >> seems > >> to have been done so admirably. > >> > >> Regards, > >> Bill Hooper > >> Fernandina Beach, Florida, USA > >> ======================== > >> SIMPLIFICATION begins with SI > >> ========================
