[ARC5] The International System of Units (SI)

Sun Feb 14 21:57:00 EST 2016

In Emergency Services, we now have to speak plain language. All of these
abbreviations (and many others, especially in the law and scholarship) came
about when type and type setting was expensive. Because of all the lurking
ambiguities in abbreviations, even official ones, I try to write in plain
language and spell everything out (even for sophisticated readers, at least
at first). Our "WordProcessors" make this easy to do, throughout a note or
even big document. The extra electrons don't mind. Readers may appreciate
it.

Reading confused and confusing old diagrams is another issue...

73

##

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On Sun, Feb 14, 2016 at 11:37 AM, Richard Knoppow <1oldlens1 at ix.netcom.com>
wrote:

>     There are a lot of not quite correct conventions especially in some
> old schematics. For instance mmf for micro-micro farad now more commonly pf
> and the prefix m for one thousand ohms usually with "meg" for megohms.  The
> latter can be quite confusing if you are not familiar with it. Vacuum tube
> diagrams were all over the place.
>
> On 2/14/2016 6:54 AM, J Mcvey via ARC5 wrote:
>
> That's all well and good, but who has a greek character font that they can
> readily inject into their text? Thus the convention of using "u" for mu?
> I never had a problem understanding the usage in that context. It's better
> and less confusing than m which is more universally used to denote milli.
> Since that was the case, why did they ever use mfd for microfarads when
> ufd kind of looks like mu and is now universally understood as such?
> Where you can get tripped up with mHz (milli hertz) vs MHz (megahertz) ,
> but that too can usually be figured out in the context.
>
> There are lots of backwards conventions, like current flow diagrams,etc,
> but at the end of the day, it does the same thing so it doesn't matter.
>
> New or old way.I can get through it OK.
>
>
>
>
>
> On Sunday, February 14, 2016 8:42 AM, Roy Morgan <k1lky68 at gmail.com>
> <k1lky68 at gmail.com> wrote:
>
>
>
> On Feb 14, 2016, at 5:50 AM, Leslie Smith < <vk2bcu at operamail.com>
> vk2bcu at operamail.com> wrote:
>
> Re: [ARC5] The BC-221 low frequency tank circuit puzzle.
>
> > ... - the 10.4 uH vs 10.4mH difference nicely illustrates one of
> > my pet peeves.  This is  a failure to distinguish corretly between unit
> > designators.  By this I refer to those pesky prefixes - such as "u"
> > (properly mu, not "u") or 10e-6 and "m" (milli, one one-thousandth),
> > Mega (x10e6)  and so on.
>
> (From an earlier post I made on the Collins list, and expanded for this
> post):
>
> > …  By the way GHz is spelled GHz and not Ghz!
>
> For the authoritative standard way to use abbreviations of this sort, see:
>
> http://www.nist.gov/pml/div684/fcdc/si-units.cfm
> International System of Units (SI)
> "The International System of Units (SI) provides definitions of units of
> measurement that are widely accepted in science and technology …”
>
> Guides to the SI:
> ...
> A practical description of the SI is Guide for the Use of the
> International System of Units (SI), 2008 ed. (U.S. Government Printing
> Office, Washington, DC, 2008) [NIST Special Publication 811].
> http://www.nist.gov/pml/div684/fcdc/upload/sp811.pdf
>
> Wherein you will find:
>
> Table 3. The 22 SI coherent derived units with special names and symbols.
>
> Derived quantity  Special name  Special symbol
> ...
> frequency  hertz  Hz
>
> (Note: Table 3 contains many of the units named after famous persons such
> as Newton and Pascal.  I was under the impression that most, but not all
> symbols for such units are capitalized but that at least one was not.  I
> cannot find that example however. The “special names” in Table 3 are not
> capitalized except for “degree Celsius".)
>
> and
>
> Decimal multiples and submultiples of SI units: SI prefixes
> Table 5.  SI prefixes
>
> Factor Prefix Symbol
> …
> 10 ^ 9 = (10^3)^3  giga  G
> and
> 10^-6 = (10^3)^-2 micro m(in the table this character is greek letter
> lower case mu)
>
> I searched for the abbreviation “mu” that we associate with permeability
> and found
> "Certain quantities, such as refractive index, relative permeability, and
> mass fraction, are defined
> as the ratio of two mutually comparable quantities and thus are of
> dimension one”
>
> 7.10.1 Decimal multiples and submultiples of the unit one
> Because SI prefix symbols cannot be attached to the unit one (see Sec.
> 6.2.6), powers of 10 are
> used to express decimal multiples and submultiples of the unit one.
>
> Example : mr = 1.2 3 1026 but not : mr = 1.2 m (the “1026” is not
> correctly rendered here_
> Note : mr is the quantity symbol for relative permeability.
>
> (In the document the “mr” above appears as the greek letter lower case mu
> with the subscript of the greek letter capital tau- I think)
>
> Roy
> Retired NIST employee
>
> Roy Morgan
> k1lky68 at gmail.com
> K1LKY Since 1958
>
>
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> --
> Richard Knoppow1oldlens1 at ix.netcom.com
> WB6KBL
>
>
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