The millimetre is a prefixed SI unit. D. -----Original Message----- From: [EMAIL PROTECTED] <[EMAIL PROTECTED]> To: U.S. Metric Association <[EMAIL PROTECTED]> Date: March 28, 2002 12:41 Subject: [USMA:19123] What is an SI unit?
> 2002 March 28 >What is an SI unit? >In 19104 Bill Hooper says "The litre is not an SI unit." Well, yes it is. >This long-time problem arose even more strongly with the millimetre. Could >we >really get away with telling people that the millimetre is not an SI unit? >We would >be laughed out of town. Or people would say to hell with SI. > >The CCU has treated this issue. Any unit, with a prefix or not, formed from >the >base and derived units is an SI unit. Accordingly, Section 2.2 of draft 5 of >SI10 >now says > > "The term SI units includes the SI base units, the SI derived > units, and all units formed from them using the SI prefixes. > >The coherent property applies to units without prefixes. > >The second paragraph of Section C.1, called C.1.1 in draft 5, has the word >"coherent" added to the text to read: > > "A great advantage of SI is that there is one and only one > coherent SI unit for each physical quantity." > >Furthermore, what is the meaning of a requirement that SI units be used? >Section 3.3.2 Units in use with SI says: > > "Compliance with this standard includes the use, as needed > and convenient, of certain non-SI units listed in Tables 6 > and 7, as well as all the SI units, including the multiples > and submultiples." > >This makes it now easier to promote SI units. > > Robert Bushnell, PhD PE > meteorologist > chair ASTM E43 on SI >
