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'[OT] Units [Was: Beginners Problem ??]'
1999\03\13@005719 by

On Fri, Mar 12, 1999 at 11:12:49PM -0500, Wagner Lipnharski wrote:
> Hi Biswanath,
>
> I don't want to be a pest in your life, but by the fact
> that you are learning, you would understand if I correct
> you in few things, and I am sure some other people
> around will learn it too.

Sadly, there are competing "standards", which may not
come from electronics per se but are a fact of life
nonetheless. Many corrupting influences of course come
from the vile world of computers, still somehow part of
electronics, no? :-)

>  milli (m) 0.001
>  micro (µ) 0.000,001
>  nano  (n) 0.000,000,001
>  pico  (p) 0.000,000,000,001
>  deca  (d) 10
>  centi (c) 100
>  kilo  (k) 1,000

Yes, but kB always looks wrong, so in discussing memory
capacity KB is not incorrect. In this context, of course,
K is 2^10 instead of 10^3 anyway, so perhaps this is not
a contradiction.  Still, with this excuse, M meaning 2^20
and G meaning 2^30 result in a bit (NPI) of a conundrum.

>  Mega  (M) 1,000,000 (upper case because the -m- milli)
>  Giga  (G) 1,000,000,000 (upper case because -g- gram)
>  ...others
>
> For example, milli is just "m" it is not an abreviation
> form, so it does not carry the dot "m."
> Start using the right denomination as much as possible
> and quickly you will do it without any effort.

Of course, again in the context of computers, "b" is
"bit" (0 or 1), while "B" is "byte" (eight bits). Thus
we get "Kb" for 2^10 bits and "KB" for 2^13 bits, although
one of course on occasion sees "kb" for 2^10 bits, as
though the "K" needed to step down out of pity for the poor
little bit. But surely "MB" is 2^23 bits, and "Mb" is 2^20
bits, and, my all-time favorite when it appears in
print, "mb" is 0.001 bits. I'm still trying to figure
that one out.

> 10kOhms, or R10k, not 10K, someone can confuse it with
> 10 Kelvin degrees.

In this case, I will disagree. If 10kOhms can't be written
"10K", then certainly 10 degrees Kelvin has no greater right
to go around naked like that -- at least it needs to have
the ¡, out of fairness if nothing else. But seriously, "K"
by itself is not, AFAIK, assigned to *any* unit if measure;
degrees Kelvin is ¡K, beginning and end of story; if you
cannot write the ¡ symbol, use the word "degree". Horowitz
and Hill argue vehemently that "10K" is unambiguously
10kOhms; the argument for this is that resistance is the only
unit so fundamental to the study of electronics that it
can be unambiguously stated without the use of the Omega
or word Ohm. It is a judgement call whether or not to go
along with this, but the potential for confusion with Kelvin
isn't a valid argument against it, IMHO. The common usage
of "5R1" for 5.1 Ohms and "5K1" for 5.1 kOhms is similarly
contestable, but seems fairly well ingrained even in the
labling of, say, 1% resistors.

{Quote hidden}

As we drift out of symbols for units and into
physical constants, "G" is the gravitational
constant, approximately 6.6732x10^-11 N-m^2/kg^2,
whereas "g", the acceleration due to gravity,
is approximately 9.80621 m/s^2 at 45¡ latitude.

(Note that, if a multiplicative prefix is used in
a unit specification, (mA, or cm, for example), then
a following exponant (e.g. cm^2) unambiguously
applies to the entire combination, i.e. cm^2 is
square centameters, not centasquaremeters.) Also,
if units are combined, as in N-m for Newton-meters,
a hyphen or a solidus should almost always be used,
but no more than one solidus -- cm/s^2 is OK but
cm/s/s is not.

> Degrees use the "¡" symbol, as ¡F or ¡C, to type it
> just press and hold ALT+SHIFT and type 0 1 7 6 at the
>
> The same for "µ" ALT+SHIFT+0181 (not 181)
>              "¸" ALT+SHIFT+0189
>              "¹" ALT+SHIFT+0188
>              "²" ALT+SHIFT+0190

This, I am afraid, depends greatly on one's choice
of text editor and, perhaps, operating system.

BTW, in preparing this response, I made extensive
use of my trusty "Rubber Bible" -- the CRC Handbook
of Chemistry and Physics, 55th edition, which is
frighteningly dated 1974 (and purchased new by myself,
I must add). I wish to report that Wagner's statement
of the rules for SI multiplicative prefixes is exactly
in agreement with that text, right down to "k" being
lower case and "M" being upper.

In good humor,

--Bob

--
============================================================
Bob Drzyzgula                             It's not a problem
============================================================

Hi Bob,

At 12:55 AM 3/13/99 -0500, you wrote:
[SNIP]
>the ¡, out of fairness if nothing else. But seriously, "K"
>by itself is not, AFAIK, assigned to *any* unit if measure;
>degrees Kelvin is ¡K, beginning and end of story; if you
>cannot write the ¡ symbol, use the word "degree". Horowitz

Well,Bob,in some of my Physics classes, Kelvins have been considered to be
a unit unto themselves (IOW, it is correct to say 10 Kelvin instead of 10
degrees Kelvin) It seems to me that there isn't real agreement on this
point. It is probably not a really good way to differentiate,but how about
the fact that usually, with resistance, the K is written right next to the
value (i.e. 10K or 10k) and with temperatures, there is usually a space
(i.e. 3 K cosmic background radiation).

>BTW, in preparing this response, I made extensive
>use of my trusty "Rubber Bible" -- the CRC Handbook
>of Chemistry and Physics, 55th edition, which is
>frighteningly dated 1974 (and purchased new by myself,
>I must add). I wish to report that Wagner's statement
>of the rules for SI multiplicative prefixes is exactly
>in agreement with that text, right down to "k" being
>lower case and "M" being upper.

I've got the 1992-93 edition,but it seems to me that most of the material
from it greatly pre-dates 1992 anyway,with the exception of the 1983 (IIRC)
accepted constants. The CRC handbook really comes in handy because I can be
pretty sure that if a prof. says "look it up",its in there! I didn't buy
it,got it as a prize in a Chemistry competition.

{Quote hidden}

| Sean Breheny
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
shb7cornell.edu ICQ #: 3329174

At 00:55 03/13/99 -0500, Bob Drzyzgula wrote:
>In this case, I will disagree. If 10kOhms can't be written
>"10K",

of course it can, and mA can be written Mamps... as long as you stay within
a =small= context, everybody'll understand.

>then certainly 10 degrees Kelvin has no greater right
>to go around naked like that -- at least it needs to have
>the ¡, out of fairness if nothing else. But seriously, "K"
>by itself is not, AFAIK, assigned to *any* unit if measure;
>degrees Kelvin is ¡K, beginning and end of story;

nope. i don't know where the beginning of the story is, and i certainly
don't know where the end will be, but "K" is the unit "Kelvin" for the
absolute temperature in the SI ("Systme Internacional") -- no "¡", no
"degree". Celsius, Fahrenheit and Reaumur use ¡, though.

{Quote hidden}

i still don't understand why you insist in using the upper case "k". it
sounds everything fine, except for the upper case. =my= keyboard, at least,
makes it even more comfortable to write 5k1 than 5K1. and i agree
completely with you that for resistors, capacitors and inductors the form
to write 5k1 or 4u7 is in most cases pretty unambiguous, especially when
used in a schematic. and it's a whole lot safer against misreading than
5.1kOhm -- the dot sometimes gets pretty tiny.

>square centameters, not centasquaremeters.)

right, but it's "centimeters" (also in english, i think, but i'm no native
speaker :)

ge

On Sat, Mar 13, 1999 at 01:47:41AM -0800, Gerhard Fiedler wrote:
> At 00:55 03/13/99 -0500, Bob Drzyzgula wrote:
> >In this case, I will disagree. If 10kOhms can't be written
> >"10K",
>
> of course it can, and mA can be written Mamps... as long as you stay within
> a =small= context, everybody'll understand.

I was mostly referring to the ommision of the unit,
rather than the case of the "K", but you are right about
the inconsistancy in my use of case. My only defense is
that I wrote that *way* past my bedtime :-) This
correction, of course, only lessens the risk of confusing
10k as a resistance and 10¡K as a temperature.

{Quote hidden}

Then you know something that I didn't. As my reference
here, I was using the CRC Handbook, which distinctly
and consistantly uses the ¡K in its telling of the SI
standard. The CRC Handbook also points out that, when
speaking of a temperature *interval*, the indication of
Kelvin or Celsius is irrelevent (being different only in
offset) and thus it is considered proper to use only ¡,
"deg" or "degree" in stating an interval when the scale
is clear from context. Thus, from this I concluded that
it is the ¡ that is considered the primary symbol for
temperature, with "F", "K" and "C" being suffix indicators
for scale and offset. I suppose that this could reflect
the age of my copy? Perhaps someone has the source standard
and can clear this up?

Of course, the very same handbook then goes and violates
its own advice in several other sections, using K by itself
for example in the statement of the units in Boltzman's
constant. I take this to mean that the use of the ¡ is
offical and proper, but it is a pain in the behind to
carry around all the time so everyone just winks at each
other and omits it when they can get away with it. But
it also could mean that the CRC's statement of the SI
standard is incorrect.

> >Horowitz
> >and Hill argue vehemently that "10K" is unambiguously
> >10kOhms; the argument for this is that resistance is the only
> >unit so fundamental to the study of electronics that it
> >can be unambiguously stated without the use of the Omega
>
> i still don't understand why you insist in using the upper case "k". it

Because the last thing I was looking at did it that way
and I didn't think sufficiently about it. Looking at several
other references I see now that the lower case is much more
frequently and correctly used; I stand corrected.

> >square centameters, not centasquaremeters.)
>
> right, but it's "centimeters" (also in english, i think, but i'm no native
> speaker :)

Correct, thank you. I never could spell worth a damn. :-)
Of course, it is "centimeters" in "American" but probably
"centimetres" in "English"? :-)

--Bob

--
============================================================
Bob Drzyzgula                             It's not a problem
============================================================

At 07:57 03/13/99 -0500, Bob Drzyzgula wrote:
>> nope. i don't know where the beginning of the story is, and i certainly
>> don't know where the end will be, but "K" is the unit "Kelvin" for the
>> absolute temperature in the SI ("Systme Internacional") -- no "¡", no
>> "degree". Celsius, Fahrenheit and Reaumur use ¡, though.
>
>Then you know something that I didn't. As my reference
>here, I was using the CRC Handbook, which distinctly
>and consistantly uses the ¡K in its telling of the SI
>standard.

look at http://physics.nist.gov/cuu/Units/units.html where they tell a bit
of the SI story (it's one of the top links of a web search on "units si",
so it's not exactly hard to find anytime you might need it :). your
handbook seems outdated.

the difference is, as i see it, that Kelvin is an absolute unit, and
therefore a "real" physical unit, and has no ¡. whereas the various "human"
temperature scales are just that, and so they get the traditional ¡ in
front of them.

ge

Gerhard Fiedler wrote:
> look at http://physics.nist.gov/cuu/Units/units.html where they tell a bit
> of the SI story (it's one of the top links of a web search on "units si",
> so it's not exactly hard to find anytime you might need it :). your
> handbook seems outdated.
>
> the difference is, as i see it, that Kelvin is an absolute unit, and
> therefore a "real" physical unit, and has no ¡. whereas the various "human"
> temperature scales are just that, and so they get the traditional ¡ in
> front of them.
>
> ge

so I was right since the beginning. :))

Degree means basically rotation in a scale, and so it was in the old
thermometers, a torsion device based on temperature.  Each one build
its own scale, so entitled it with his name. A whole degree in each
one was meaning different temperatures, based on the way it was
build.  Different from Kelvin that is an absolute physical unit.
I use a thermometer microchip that gives me Volts/Kelvin, easy,
pure, no crazy conversions or factor tables.
Wagner

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