Talk:International System of Units/Archive 1

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Besides USA who doesn't use SI

Which countries besides US do not use SI units in everyday life? AxelBoldt

That depends in part on definitions. Britain has finally gone metric for most purposes, but have an indefinite exemption for a few things, such as selling beer by the pint, not the liter or half-liter. Hong Kong is SI, except when they're selling fruit by the catty at outdoor markets. I suspect there are other such. Vicki Rosenzweig
Ok, then: are there other countries where non-metric units are used as extensively as in the US? AxelBoldt
I'm pretty sure that no other coutry in the world uses non-metric units as extensively as in the US. However, in some english speaking countries, the size is measured in foot-inches (at least in Canada, and partially in the UK).
Interestingly enough, in some specific area, the measurements are non metric in metric countries. For instance screen diagonals (for TVs and computer screens) and floppy disks sizes are measured in inches, heights when flying in a plane are measured in feet, height of bicycles are in inches in Europe. The speed limits are in mph in Ireland.
Another interesting phenomenon is the adjustment of ancient measurement units to the metric system. For instance, the french pound ("livre") has been adjusted to 0.5 kg and the swedish mile ("mil") has been adjusted to 10 km. Chtito 09:00, 4 Sep 2004 (UTC)
Additionally in Britain, miles are still used for distance and miles per hour for speed on roads. The height and weight of a person is still de facto a imperial measurment, depsite official attempt to mchange to metric. All medical forms will give the option of imperial or metric as most Britons do not use metric in this specific area. Addtionally the height and weight of boxers is still expressed in imperial terms. The major difference to the US system is the use of Stones (units of 14 pounds) in personal weight. For Example, a 175 pound person would say they are "12 stones, 7 pounds" or more likely in speach "twelve and a half stone" (using the singular noun).
Dainamo March 14,2004
To add to that, horse heights in the UK are officially given in "hands", which are units of 4 inches. --Delirium 06:33, Jun 10, 2004 (UTC)
And just to make things exciting, the company I worked for once had some Japanese engineers ask for test results in pounds per square millimeter. --Carnildo 19:51, 27 Oct 2004 (UTC)
That actually isn't so spectacular, for many scientific and technical applications, older units are still commonly in use. For example, in the vacuum industry, the use of Torr is as common if not more common than the use of bar, whilst some tubes are still commonly measured in terms of inches. And this happens all over the world, so I don't find it surprising it happening in Japan also. As far as I know, the USA still is pretty much the last country with widespread use of the non-metric system (and dosen't seem to want to change either...).--Vertigo200 06:13, 22 Jun 2005 (UTC)

I have a friend who was raised in France, speaks French and is a college-educated automobile mechanic who in 25 years went through the transition from Imperial to metric system with several lines of cars, including teaching it to other mechanics, and he has never heard the expression SI. Hence, I added the word "metric" to this article. Ortolan88

Wait a minute here. I thought that the cgs system is what is commonly called the metric system and SI is simply the International Standard used by scientists (based on m, kg, s)? I also thought that most nations use a hybrid system made up of SI and cgs units. If the opening paragraph is correct then temperatures in Europe are measured and displayed in Kelvin and not degrees Celsius. --mav

I was going by the metric article and the metric-fan additions to Wikipedia:Manual of Style. It seems both these articles are wrong, from what you say. Every time I try to speak up for the 260 million non-metric Americans, I am treated to a condescending lecture on how superior the metric system is. I have never said it isn't superior (except for temperature), but that isn't the issue. The issue is ease of use of the wikipedia by the world's largest internet nation. It is too damn bad the US has been so slow and reluctant and whatever to adopt the metric system, and it is slowly coming in now, but we still don't use it in everyday life, so if we want to know how tall a hippopotamus is, someone is going to have to help us out. It is with some schadenfreude (delight at the discomfort of those you disagree with) at this indication that even metric enthusiasts are not sure what the difference between metric and SI is. Ortolan88

The SI system is a metric system. So are cgs and MKS (referenced in the article International System of Units). (I wouldn't call any temperature scale "metric", though.) See the Origin of the metric system section of the History_of_Weights_and_Measures page. --Zundark 08:31 Sep 16, 2002 (UTC)
indeed. SI is a choice of base units from the overall system. It also determines the sizes of all the derived units, such as Newton, Joule etc (instead of Dyne, etc), so it's fair to say that the SI system is what we use nowadays. In everyday use, whether one choose cm, mm or m to express a measurement doesn't really matter. -- Tarquin

Ortolan88, your point is taken, but I consider basic comprehension of metric units to be a matter of literacy. Any article must make some assumptions about what the reader already knows, and I personally hope that the articles in wikipedia will be written with somewhat more sophistication than newspaper articles (which I've heard are at a 9th grade level). If a person has no idea what it means that cheetahs weigh 150 to 300 g at birth, I think they should figure it out. -- Cos111 01:13 20 Jul 2003 (UTC)

Ortolan88, also students in America are taught SI units in middle school and high school according to the National Science Education Standards. Unfortunately, since it is not reinforced in the greater society, most of us remember it just long enough to pass our standardized tests, then wipe it from our minds forever. Research scientists in the US typically use SI units, but engineers don't. --zandperl 17:39, 17 Mar 2004 (UTC)

All the engineers I know (here in the US) would be brutally executed for failing to use SI units. --Dante Alighieri | Talk 18:18, Apr 19, 2004 (UTC)
Electrical engineers in the US use SI. But in studying rocketry about 15 years ago, I was shocked to find that rocketeers use English units. --cameronc 19:08, 15 July 2004 (UTC)
That's because the units are so much simpler to work with -- one pound of thrust applied to one pound of mass provides one gravity of acceleration. --Carnildo 07:47, 21 Dec 2004 (UTC)
Let's not forget the US space craft (I forget the name) that was lost because one contractor used metric, the other English. As you can believe from the above comments. 64.168.30.87 06:47, 21 Dec 2004 (UTC)

The question is more complicated than this. As mentioned above, in many countries people use here or there an imperial unit generally without knowing what it means. Best examples are pipe sizes and computer screen sizes. The true question is which governments have not yet adopted SI as their national system of units. To my knowledge there are only two: Liberia and Myanmar. More info here. Also, one may be surprised to find out that the US has adopted the SI since 1867 and is a full member of the Metre Convention. The reason SI is still not widely used has to do more with poor implementation. Sadly enough many Americans also relate their system of units to their patriotic duties. More detailed info on the history of US metrication may be found on the US Metric Association's website. Metricus 2005-06-01

Metric Units are not SI Units

Although SI units are (largely) based on the Metric system they should be considered distinct as there are notable differences: Temperature: SI= Kelvin; Metric =Celsius Volume: SI = dm3; Metric = liter/litre (these are not the same as would first appear as a liter of distilled water and kg of distilled water are the same thing and the volume in SI units will vary with temperature). Distance: SI = metres only, Metric versions such as Km, cm etc. are not permitted. similar to weight in SI where it is always measured in Kg. grams, Tonne atc. not used. Energy is always in Joules in SI units -never Kcal. Additionally some non-metric units are SI units such as s (seconds). Attempts for a metric time measurment were, for obvious reasons, abandoned shortly after the French first considered it. Dainamo March 14,2004

The SI most certainly does permit km, cm, etc. They are SI derived units, a standard part of the system and notated with SI prefixes. They are not SI base units, but they are part of the system. For the purpose of allowed units, SI is the same as all other metric systems; the only thing that differs is which are considered the base units and which are considered the derived units, which is unimportant in practice (it's only important for the definition and maintenance of reference values). --Delirium 02:13, May 25, 2004 (UTC)
You are indeed correct in the above observation, however that does not deflect from the fact that, although based largely on the metric system, SI units should not be considered as the same thing. Liters/Litres, Celcius are two measures not permitted as SI units and the SI units of seconds is never metric. Furthermore there are other fundemental differences such as Kg being a metric measure of weight but of mass in SI units. The concept of weight relies both on mass and gravatational force which are different. Hence a 60kg man may say he remains 60kg on the moon in SI units but he would not be incorrect to say he "weighs" appropriately less in Kg in using metric due to the reduced gravatational force. I am not being pedantic but a distinction between the systems is needed to avoid potetnial inaccuracy
By the way, the litre and the dm3 are exactly the same, and have been since 1964. --Jeepien 17:22:20, 2005-08-04 (UTC)

I think "SI" is a better page name that "International_System_of_Units" -- a huge number of articles here refer to it as SI. Principle of least astonishment etc -- Tarquin 21:57 Jan 8, 2003 (UTC)


Just a little something about the transition from imperial to metric: I have on several locations/occations in Australia seen various 'metric' notations...
Example: "75 sqklms land for sale!" Instead of much simpler 75 km2
-- Gorm

I think this is due to people not being able to type km2 (This is common in cases where the ad is produced from information stored in a database). - 211.28.160.221
That still is a rather redarded way to abbreviate km²; km*km would be much preferable. Of course, if one wanted to be funny, one could always write km² as GL/m. Mkweise 01:27, 18 Nov 2003 (UTC)

Base units

I see that the SI base units have a separate page, however I'd also like to see them listed briefly here, perhaps in table form. Is there a reason I shouldn't do so? --zandperl 17:30, 17 Mar 2004 (UTC)


[Comment deleted by its original poster, who evidently cannot read. Never mind.] --Suitov 15:02, 6 Apr 2004 (UTC)


Disagreement over the way to write numbers

The latest change suggests this usage:

The symbol (or prefix) can be used in place of the decimal seperator. 2.3k would be 2k3, 4.7A (Amps) would be 4A7, and 0.0047F would be 4m7F.

I cannot find any justification for this statement in the BIPM brochure "The International System of Units (SI)" at URL http://www.bipm.org/utils/en/pdf/si-brochure.pdf nor in the NIST document http://physics.nist.gov/Document/checklist.pdf. Absent any justification, I think this statement should be deleted. Comments?

The word seperator has been spelled incorrectly, in any event. It should be separator.

cbc 09:11, 22 Jul 2004 (UTC)


The xky convention is widely used in the electronic/electric area, so a 4k7 resistor is a 4,700 Ohm resistor, but have neve seen any reference to this being ruled by the SI. -- Poli 18:17, 9 Mar 2005 (UTC)
Any use of the SI units is governed by the rules for use of the SI units. The fact that "ohm" should be lowercase in your example is governed by the rules of the English language. Gene Nygaard 21:31, 9 Mar 2005 (UTC)
All of the metric units are rendered uncapitalized when spelled out as the name of the unit, even the dead-white-guy names. The single exception to this is the "degree Celsius". I agree the oddball infix use of prefixes should nipped in the bud.

Radian / steradian as derived unit

Radian and steradia are listed under "Dimensionless derived units": "The following SI units are derived from the base units and are dimensionless."

How can they be considered "derived from the base units" since those unit don't appear in their definition?

The radian is condsidered to be derived from m/m and the steradian from m²/m². The text says they "do not require the definition of a base unit". But the [| Brochure] says, "The unit of such quantities is necessarily a derived unit coherent with the other units of the SI and, since it is formed as the ratio of two identical SI units, the unit also may be expressed by the number one." It is not strictly necessary that the "base" units for a radian even be metric at all. It could just as well be measured in feet. But without any unit, you will have nothing to divide in order to calculate your ratio. Any SI definition naturally would require that SI units be used in caclulating the "lengths" and "areas" needed to determine the angles. But by nature of the definition, the result in radians then becomes independent of the system originally used to calculate it. --Jeepien

Prefixes

How is it that there is no table or elaboration on the different standard prefixes deca, hecto, kilo, etc...??

Derived units table

The table of derived units is inconsistent about whether to use the solidus ("/") or negative indices, but I'm too lazy to fix it myself. Anyone? ,,,Trainspotter,,, 22:43, 21 Sep 2004 (UTC)


Invention of the SI / Metric System

Did Simon Stevin invent the idea of Metric systems in 1585 in his book 'De Theinde' - predating the current article's promotion of the French invention in 1640? Should the article be amended to reflect this historical point? Ian Cairns 22:51, 17 Oct 2004 (UTC)

Simon Stevin advocated the idea of using decimals for monetary and measurement purposes, but he didn't invent the idea of Metric systems. --PieIsIrrational 07:17, 21 Nov 2004 (UTC)

Should the claim for 1640 be the idea of a decimal system of measurement, not the metric system? After all, Thomas Jefferson's decimal system isn't metric either? Septentrionalis 14:52, 13 May 2005 (UTC)

Recent changes by Dainamo and JimWae

Changes by Dainamo:

Dainamo's claims above that "grams" and "kilometres" are not SI are nonsense. Apparently he or she has seen the light now (see the dm³ comment below), but I'm just making that point here rather than addressing it again in the comment above

Changes by Danaimo on 16:04, 6 Jan 2005

replaced

 Metric system is a broader term which includes SI; however, not all 
 metric units of measurement are accepted as SI units.

with

 Strictly speaking the International System of Units refers to a specific
 canon of measurements derived and extended from the Metric System. For 
 example the SI unit of time, and all other units based on it is the second,
 which is not a metric unit. Additionally some metric measurements such as
 the liter or degrees Celsius are not SI units (dm3< and
 degrees Kelvin would be used in place of each of these). 

then on 16:26, 6 Jan 2005

replaced same part with

 Strictly speaking the International System of Units refers to a specific
 canon of measurements derived and extended from the Metric System. For
 example the SI unit of time, and all other units based on it is the
 second, which is not a metric unit. Additionally some metric measurements
 such as the litre for volume or Celsius for temperature, while
 specified now as acceptable (see below) are not SI units (dm3
 and Kelvin are the proper SI units for each of these respectively)

My comments, not terribly well organized, and with intentional overlap:

  1. The degree Celsius is SI. It is listed in the BIPM's SI brochure in Table 3: SI derived units with special names and symbols. The litre is in a different table of units acceptable for use with SI.
  2. That the SI extended previous versions of the metric system does not mean that those extensions are not part of the "metric system."
  3. SI is a subset of the "metric system", and the associated collection of rules for its use—nothing more and nothing less. Everything in SI, and every change to SI, supplements and changes the broader, inclusive term "metric system."
  4. "Metric system" and "SI" are by no means mutually exclusive terms.
  5. Even after the SI was introduced, the CGPM redefined the liter, a non-SI unit.
  6. When the CGPM told us to stop using the "micron" and the "degree Kelvin" that applies just as much to those dinosaurs in certain branches of physics and astronomy who cling to the cgs systems as dearly as Americans cling to their inches and pounds.
  7. Similarly, I have seen people claim that "gm" remains an acceptable symbol for grams when the cgs systems are used today; I don't buy that.
  8. The SI prefixes are very much a part of the SI (see Danaimo's months old and probably no-longer-maintained claims above that "grams" and "kilometres" are not SI).
  9. The other SI unit of temperature, the base unit, is the kelvin (plural kelvins), not "degrees Kelvin" and not just "Kelvin" with a capital K in English (however, these are rules of the English language, not rules of the SI; it, like the other units, is capitalized in German, for example).
  10. Seconds are a non-SI unit borrowed into SI. An ancient Babylonian unit, to be precise. That borrowing by SI does not remove them from any other subset of the "metric system" nor from the "metric system" in its general, broad sense. Nor does that borrowing for use with SI eliminate them from any "English system." Furthermore, it does not mean that everybody using any of those other systems of units needs to maintain their own standards for the second. It is quite proper and legitimate for them to borrow the SI standard.

Changes by JimWae:

Virtually all non-SI units have been redefined in terms of SI units. 
  

That isn't true. I'll buy "most."

  1. When my doctor measures my lung pressure in cmH2O, those units are not defined in terms of SI units.
  2. Some flavors of calories, and some flavors of British thermal units, are defined in terms of SI units, or at least in a way that can be expressed exactly in SI units. Others are not.
  3. Some of the various "tons of coal equivalent" and the like are defined in terms of SI units, others are defined in terms of those Btu or calories, just as "therms" (with various legal definitions for different applications and jurisdictions) and "quads" are.
  4. Solar masses are not defined in terms of SI units.
  5. Parsecs and astronomical units are not defined in terms of SI units; though there may be conventional values used which change over time, the astronomical unit is still essentially considered to be a measured quantity with error bars in the accuracy of its measurement.
  6. Pounds force are not officially defined in terms of SI units. Each of the various definitions in actual use can probably be converted exactly to SI units, but there is no general, official designation of one of those units, as there is with pounds as units of mass. See, e.g., the conditional definition with a great big "if" in the appendix of conversion factors in NIST Special Publication 811, footnote 24 which links to separate page in html version, [1]
  7. The day, week, month, etc., retains several definitions. However, JimWae himself took out a reference to a redefinition of the day in terms of SI units, viz.

JimWae 14:05, 6 Jan 2005 from

The metric unit of time remained the second. 
One definition of day is 86,400 seconds. 

to

The metric unit of time became the second, originally defined
as 1/86,400 of a mean solar day. 

Different meaning entirely. The problem here is that this changes the the whole orientation of the original, removing any reference to any current definition of a day. The solar day fluctuates quite a bit. Using a day of 86,400 seconds has replaced older attempts to try to define a day by measuring a "mean solar day" over some specified period of time.

JimWae changes 14:05, 6 Jan 2005

From

The unit of mass is the kilogram, which was defined by a cube 
filled with distilled pure water at its densest (+4° Celsius) 
and having sides equal to 1/10th of a metre. This volume contains
one kilogram of water. One kilogram is about 2.2 pounds. This 
cubic space was also known as one litre (since slightly revised) 
so volumes of different liquids could be compared. Later on, a 
platinum-iridium metal cylinder was manufactured to serve as the 
one kilogram weight standard and remained so ever since.

to

The original base unit of mass in the metric system was the gram, 
but was quickly changed to the kilogram, which was defined as the
mass of distilled pure water at its densest (+4° Celsius) 
contained inside a cube having sides equal to 1/10th of a metre.
One kilogram is about 2.2 pounds. This cubic space was also 
called one litre so volumes of different liquids could easily
be compared. Later on, a platinum-iridium metal cylinder was 
manufactured to serve as the one kilogram weight standard and
remained so ever since, replacing the water-based definition
of the kilogram (which had some slight inaccuracies). 
  1. That platinum-iridium cylinder was put into use way back in 1890, after the new international organizations (CGPM, CIPM, BIPM) were created by the Metre Convention of 1875.
  2. However, this particular Pt-Ir cylinder was not the replacement for the "water-based" definitions. That replacement had already taken place nearly a century earlier, when
  3. In 1799, a platinum cylinder known as the Kilogramme of the Archives, maintained by the French government, became the official standard defining the kilogram.
  4. When the CGPM had the new standards constructed, their target had nothing to do with water. The new kilograms (40-odd in all, with one picked at random for the International Prototype and most of the others becoming national standards) were constructed with the Kilogramme of the Archives as the target standard.
  5. In other words, no "water-based" standard ever held sway for purposes of defining the kilogram, except for maybe a couple of years when the metric system was being developed back in the 1790s.
  6. However, for the period from 1901-1964, the flip-flop of this idea did apply. Instead of defining the unit of mass based on the mass of a certain volume of water under certain conditions, we had a unit of volume defined as the volume occupied by a certain mass of water under certain conditions: the litre. Consequently, when the SI was first introduced in 1960, the litre was not only not a part of SI, but it was also not acceptable for use with SI. That change only happened after the definition of the litre was restored to 1 dm³ exactly in 1964.

Gene Nygaard 00:47, 7 Jan 2005 (UTC)


  1. I think the Origins section goes beyond origins quite a bit & so it becomes harder to be definitive in what is said there.
  2. Perhaps (or perhaps not) the second was part of the original metric system, but was it truly a base unit (defined independently of other time units)?
  3. The original scientific system to develop from the metric system was MKS, but the original metric system seems to have been MGS. CGS was a 2nd scientific system.
  4. SI is not a subset of original metric system -- many units have been added since (at least) the original. No body defines the metric system anymore, afaik. SI started development as a subset of the MKS system, extending it beyond its origins.--JimWae 17:56, 2005 Jan 7 (UTC)
No. SI is the modern version of the metric system. Good grief! Enter "Metric system" into the search box and hit "Go", Jim.
SI is a subset of the "metric system." Period. End of story. All the changes since SI was introduced have been changes in the metric system.
The second was a base unit of the cgs systems introduced back in the 1870s.
Nobody used mks systems until the 20th century.
The bodies which define the metric system are the ones set up under the "Metre Convention" or "Treaty of the Meter."
SI remains a mks system as well. It is a subsystem of mks, just as the electrostatic cgs systems and the Gaussian cgs system are subsystems of the broader category cgs. We have several different levels of "systems" involved here. System is like "set" in mathematics; subsets are sets, and subsystems are systems. Gene Nygaard 19:11, 7 Jan 2005 (UTC)

NIST Guide for the Use of the International System of Units (SI), (1995), &section;1.1: [2] (emphasis added)

Universally abbreviated SI ..., it is the modern metric system of measurement used throughout the world.

BIPM, 7th edition of the SI brochure, [3] (PDF version, p. 3 pdf file and p. 83 on page numbers printed on page)

Delegates from all Member States of the Convention du Mètre attend the Conférence Générale which, at present, meets every four years. The function of these meetings is to :
· discuss and initiate the arrangements required to ensure the propagation and improvement of the International System of Units (SI), which is the modern form of the metric system;

Gene Nygaard 19:53, 7 Jan 2005 (UTC)


  • for X to be a subset of Y, X cannot contain any elements that are not also elements of Y. Metric System is vague & you are stipulating a definition that is not obvious to all -- particularly when the ORIGINS section wanders.
Yes, metric system is vague and inclusive--and it includes EVERYTHING that is included in the SI. SI is a subset of the metric system; the "modern form of the metric system" as the BIPM calls it, and the "modern metric system" as NIST calls it. It really is that simple. Gene Nygaard 20:38, 7 Jan 2005 (UTC)
  • You are arguing for a specific wording that might be clear to you, but could be misleading to many.
  • There is no need to use the word subset, there are reasons not to.
  • Good grief yourself -- I do not take search engine results as definitive. Do you? --JimWae 20:04, 2005 Jan 7 (UTC)

  1. Look here { http://encarta.msn.com/encyclopedia_761561345/Metric_System.html } and tell me how calling SI a subset of metric system will not be counter-productive. "Developed from" & "extended from" gets across the idea without the risk of over-identification of the two.
  2. Look at Half-life and tell me who would find such a technically correct article or any like it of any use to anyone.
  3. You obviously are very learned in this field, but this has become a pissing contest, and neither of us is perfect. You seem to feel you own this article & anyone who edits must justify to you every single change, while you have ultimate authority. I do not have time for that.

--JimWae 20:58, 2005 Jan 7 (UTC) --JimWae 20:58, 2005 Jan 7 (UTC)

Is the candela really a base unit?

I think it is not, and that it is a derived unit, based on the Watt. -- Egil 12:35, 8 Feb 2005 (UTC)¨

Yes, it is as defined by SI (and common sense). Yes, technically, at some metaphysical level, there is probably only one basefundamental unit, a single space-time constant; but, at a certain level, we do not know or cannot easily practically measure the relationships between the units, so we stop deriving them from each other and call them base units.
You don't have to believe me. Read the canonical resolution 6 of the SI-defining 10th CGPM on the BIPM's WWW site (or their official translation into English of that resolution).
--Joe Llywelyn Griffith Blakesley talk contrib 13:07, 2005 Feb 8 (UTC)
At a philosophical level, you need seven base units for a complete measurement system, but nothing specifies what those units have to be. You could use the Newton, the meter per second, and the Joule as base units just as easily as you could use the kilogram, the meter, and the second. --Carnildo 18:16, 8 Feb 2005 (UTC)
Why 7? Do you have a reference for that?
--Joe Llywelyn Griffith Blakesley talk contrib 17:00, 2005 Feb 12 (UTC)
That's what I came up with in high school when I was putting together a particularly crazy system of measurement (base units included speed, power, and magnetic flux, and the derived unit for length included a fifth root). --Carnildo 02:01, 13 Feb 2005 (UTC)
It depends entirely on how you define 'base unit'. We can go by what is 'most natural', which is essentially making constants 1. If you use E = 1/2 m v^2 = 1/2 m d^2/t^2, and 'imperial' units (for some value of imperial) you get foot*poundforce = poundmass foot^2/timeunit^2, or timeunit^2 = foot poundmass/poundforce, and trivially poundforce/poundmass is just g. Then you get the derived time unit of around 0.176 seconds (or, from rest, an acceleration due to gravity causes velocity to be one foot per timeunit after a timeunit). Obviously, we're setting g=1. If we set enough constants to 1, we get Natural units. I'm not sure if there's another way to set universal constants to 1 (e is pretty important), but the only thing really stopping us is that we don't know G very accurately. --Elektron 00:47, 2005 Jun 1 (UTC)
You simply misunderstand what "base unit" means in the jargon of metrology. It doesn't, for example, imply any fundamental, independent standard exists for that unit. After all, the definition of the meter depends on the definition of the second. The definition of the ampere depends on the definition of the newton, a derived unit which depends on the meter, the second, and the kilogram. Note that unlke contrary to Carnildo's explanation, we don't "need" seven base units, either. There is redundancy in the current definitions; we don't really need a mole at all, for example. People have actually used three-base unit cgs systems with the units of charge equal to erg0.5 cm0.5, for another example. Gene Nygaard 19:27, 8 Feb 2005 (UTC)
  • which raises what I think is an interesting question: What is the least number of base units we presently need to do all the measuring we can now do?--JimWae 17:32, 2005 Feb 12 (UTC)
So my question should really have been Is the candela really a fundamental unit?. -- Egil 19:40, 8 Feb 2005 (UTC)


And the answer is: It doesn't matter in the least. The whole notion of a "fundamental unit" is vague in the first place, and dependent upon the choice of "dimensions", for which there is no unique choice. You couldn't distinguish an MKSC (meter-kilogram-second-coulomb) system from an MKSA system such as SI. Gene Nygaard 00:14, 9 Feb 2005 (UTC)


The cd must be defined as a base unit, rather than as a derived unit, because in order to satisfy the definition of "coherent", none of the derived units may use any numerical coefficient other than 1. Since the candela has coefficients in its definition that are other than 1, it has to be defined as a base unit. Not sure what you mean by "fundamental". --Jeepien 03:29:36, 2005-08-05 (UTC)

According to NIST special publication 330, the choice, "to a certain extent arbitrary, because it is not essential to the physics of the subject." and,"by convention are regarded as dimensionally independent." Which is to say that they just are and you are not to ask questions. You are poking here at the rather tender underbelly of the SI. The units are not, as you point out, in fact "dimensionally independent," however, we wish they were and keep them seperate to allow for accruate measurements, and convention. Another sore topic is temperature. Why are there two systems? What sense does that make? It's just like the tradiational system of fahrenheit, except that the afine transformation is simpler and people liked it, so they held on to it b/c it wasn't that bad.--Pdbailey 02:35, 23 September 2005 (UTC)

Kelvin

This prompted the establishment of a new temperature scale, called the absolute scale or Kelvin scale, which relocates the zero place but still uses 100 kelvins between the freezing point and boiling point of water.

The Kelvin scale is but one absolute scale. Then there's the Rankine scale. Also this sentence seems to imply that the Kelvin scale is in part based on the difference in temperature between the freezing and boiling points of water at atmospheric pressure. This is not the case as the article goes on to point out. This needs a rewrite. - Jim 16Mar05

It is most certainly "in part based on the difference between the freezing and boiling points of water"; pretty much totally based on that, in fact. How would you propose rewording it to make your point, that that's not what we look to to determine the size of kelvins now? Gene Nygaard 08:57, 16 Mar 2005 (UTC)

It's based on the difference between the freezing and boiling points of water to the extent that the metre is based on "1/10,000,000th of the distance from the pole to the equator along the meridian through Paris." In other words consistancy with the original centigrade scale was the aim but isn't the basis of the system. I guess I'd rewrite it along these lines.

This prompted the establishment of a new temperature scale, an absolute scale which relocates the zero point at absolute zero. It was named the Kelvin scale and was scaled with the aim of maintaining 100 kelvins between the freezing point and boiling point of water.

This is, perhaps, better. Maybe not perfect though. - Jim 18Mar05

Link to mediocre external calculator

I'm reverting the addition to a link to a conversion calculator recently added for several reasons. It's probably somebody's self-promotion, but it isn't significant even to worry about that.

  1. One isn't really necessary here. If anywhere, maybe conversion of units.
  2. Even the Google calculator offers more and is easier to use
  3. This one has nothing to recommend it over hundreds of similar mediocre calculators available.
    1. This calculator only includes simple quantities. Not even units of force are included, let alone more complicated things such as energy or pressure. All it includes is length, volume, and mass.,
    2. It is U.S.-centric even there, with unidentified "gallons" and the like the only option.
    3. It is sloppily constructed. If you click on the link to convert those unidentified gallons to liters, it prompts you for "Grams"!!!

I thinks that's reason enough to throw it out. If the proponent wants to discuss it here, fine. Gene Nygaard 18:48, 25 Mar 2005 (UTC)

SI in the United States and other countries

Local vs international measurement systems

"[SI] is used for everyday commerce in virtually every country of the world except the United States, Liberia and Myanmar"

This statement is wrong in several ways. First of all, SI is used in everyday commerce in the United States. It is just not the primary method of measurement in most cases.

For those who haven't been to America, virtually all rulers have inches and centimeters on them, And virtually all commercial products have the amounts listed in both metric and imperial units. It is widely recognized that the metric system is the "global language", or lingua franca, of measurement systems, while British imperial is the local language. All children are taught both systems in school.

The US, Liberia, and Myanmar aren't alone in maintaining a local measurement system. For example, the UK maintains a strong local tradition despite an official metric conversion effort that started in 1965. Furthermore, all former colonies of the UK have been influenced by the British imperial system, and despite converting over, all retain influences of the British system.

And what about China? "In measurement, Chinese units (Pinyin: Shìzhì, "market standard") are the units used in Imperial China, and are still used." (See: Chinese units) And how about other countries that have their own local measurement systems? Do you have evidence that every isolated island nation has completely changed over to SI units? And what about countries that have officially converted to the metric system, are you sure that the people of that country don't use local systems expensively? (The situation is comparable to the "official" language of a country vis-a-vis the languages that are actually spoken in a country.)

No accurate, encyclopedic statement can be made about the use of SI in every country until definitive information on the measuring systems of every country is obtained. If someone is willing to do the research, I say "go for it". We could use an article on Measuring systems by country.

In any case, we must avoid misleading statements and state only facts and claims that can be verifiably proven. I have heard statements before that paint America as the "only" country that isn't 100% on the metric system, but, the more these statements are objectively researched, the more obvious it is how misleading they are. The metric system is a very good system for many purposes, and makes an excellent "global measurement language", but it is not perfect for everything--local systems can and will exist. The United States may have a stronger local measurement tradition then other countries, but saying that it "doesn't use the metric system" is like saying that no Canadians speak French.

- Pioneer-12 10:06, 7 May 2005 (UTC)

I can tell you about the use in Australia. The country has gone metric almost entirely. The only noteable exceptions are beer measures in the pub. Glasses have their volumes printed on the bottom in millilitres but the sizes are based on Imperial fliud ounces (rounded off to the nearest 5 ml). A similar situation exists in Canada with their beer bottle sizes: 12 Imperial fliud ounces however the rounding this time is to the nearest ml. In Japan the only traditional measure I'm aware of is for area (the tsubo of land/floor sizes) however I think that some of the larger alcohol bottles are based on traditional sizes (though labelled only in metric). Jimp 15Jun05