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Who writes temperatures as "129 degrees"?

Anyone who correctly follows the official BIPM guidelines. The unit is "degrees Celsius," not Celsius. If symbols are used, then (/. still doesn't handle Unicode) "[degree symbol]C".

And since

And to head off your objection.

Readers should note that the official record is always that of the French text.

The french standard says

Il en résulte que la température thermodynamique du point triple de l’eau est égale à 273,16 kelvins exactement, Ttpw = 273,16 K.

french original

The first obligation of a pedant is to be technically correct.

From an authoritative and current source

It follows that the thermodynamic temperature of the triple point of water is exactly 273.16 kelvins, Ttpw = 273.16

If the BIPM can't be bothered,I don't see why the rest of us should follow your prescription.

Why is it so hard for you aspyrons to understand that the meaning of a word is often dependent on context?

Well, maybe because almost all the international standards organizations actually agree that there's a single meaning now (even though they disagreed in the past).

In a decimal context, kilo means 1000. In a binary context, it means 1024. Most of the people that pretend to have difficulty understanding this are actually making money from their 'confusion' - what's your excuse?

Look, what the GP said was factually accurate:

the IEEE, ISO and SI standards all agree that kilobyte means 1000 bytes, and megabyte means 1000000 bytes.

The IEC adopted these in 1998, leading to full adoption by the IEEE in 2005. SI explicitly defines kilo ONLY to mean 1000, and though bytes are not technically SI units, they regard any other use of the prefixes as incorrect.

The only large body that has endorsed the use of your system in the past decade is JEDEC, though they insist on capital letters, i.e., K, M, and G, instead of the standard SI lower-case. So, a kilobyte (kB) to them is actually 1000 bytes, while a Kilobyte (KB or K) is 1024.

Recently, if you read even JEDEC's standards from 2012, you'll note that they quote the IEEE standards and say the older style "frequently leads to confusion and is deprecated."

So, I don't know about the GP, but my "excuse" for following standard SI style is that basically all international standards bodies agree that "kilo" means 1000, and if you want to have a term for 1024, you should use something else.

Now, the reality of the world is that many hardware manufacturers and such still retain older deprecated usages. But GP's statement was basically accurate. There's no reason to go around insulting people when they state factual information.

You want to keep using a standard that has confused people for decades when the international standards organizations deprecate it because it's confusing? That's your choice. But what's your excuse for attacking people?

I'll probably get down modded but it is not just the technologies but the basic definitions of the SI system are pretty fucked up.

There are numerous problems, the primary being:

* the seven SI base units are not independent
e.g. the Amp depends on the definition of the kilogram ?!?!

http://www1.bipm.org/en/si/si_constants.html#figure

Quoting Dr. Xavier with my emphasis added:

"If for instance, one had to change the definition of the Kg unit, we see that the fundamental units candela, mole, Amp and Kelvin would change as well. .. So one cannot say there are seven fundamental SI units if these units are not independent of each other. The other big fault is the obvious redundancy of units. Although not very well known to all of us, at least two of the seven base units of the SI system are officially known to be redundant, namely the mole and the candela. These two units have been dragging along, ending up in the SI system for no reason other than historic ones. "

* http://www.blazelabs.com/f-u-suconv.asp

And it usually does, except for some of our basic units of measurement, which remain stubbornly stuck in the past. That's why it's an embarassment. The whooshing sound you heard is the point sailing over your head.

Umm, I'm pretty sure scientists have been working on the kilogram problem for some time. Your use of "stubbornly" implies that there's some sort of resistance to a redefinition. But I don't think there's any evidence that that's the case.

Here's a NYT article from 2003 detailing the then-current attempts at redefinition. I'm sure there are older things out there detailing the scientific efforts to work on this problem, too... this was literally one of the top three hits in an internet search.

Anyhow, in 2005, the International Committee for Weights and Measures formally recommended a redefinition. In 2011, the General Conference on Weights and Measures agreed. If you want to see all the proposed revisions, they are nicely summarized in a Wikipedia article here.

It may be somewhat true that the kilogram redefinition lagged a bit behind other units, mostly because the other units had practical applications where the need for increased precision was rising more rapidly. But given that the attempts to provide a standard measurement system are ongoing, and the proposed redefinitions make use of technology that is still being refined to maintain a high-enough level of accuracy to supersede the old standard, there's no reason to call this an "embarrassment" "stubbornly stuck in the past."

Scientists are actively working on the problem -- and have been for quite some time.

And it usually does, except for some of our basic units of measurement, which remain stubbornly stuck in the past. That's why it's an embarassment. The whooshing sound you heard is the point sailing over your head.

Umm, I'm pretty sure scientists have been working on the kilogram problem for some time. Your use of "stubbornly" implies that there's some sort of resistance to a redefinition. But I don't think there's any evidence that that's the case.

Here's a NYT article from 2003 detailing the then-current attempts at redefinition. I'm sure there are older things out there detailing the scientific efforts to work on this problem, too... this was literally one of the top three hits in an internet search.

Anyhow, in 2005, the International Committee for Weights and Measures formally recommended a redefinition. In 2011, the General Conference on Weights and Measures agreed. If you want to see all the proposed revisions, they are nicely summarized in a Wikipedia article here.

It may be somewhat true that the kilogram redefinition lagged a bit behind other units, mostly because the other units had practical applications where the need for increased precision was rising more rapidly. But given that the attempts to provide a standard measurement system are ongoing, and the proposed redefinitions make use of technology that is still being refined to maintain a high-enough level of accuracy to supersede the old standard, there's no reason to call this an "embarrassment" "stubbornly stuck in the past."

Scientists are actively working on the problem -- and have been for quite some time.

Caesium clocks, upon which the second is defined, differ in frequency, due to gravity, electromagnetic fields, etc. (the definition of the second is based on a Cs atom at 0K, at rest, which isn't realizable in practice). Because of this, official time is only known after the fact, based on a weighted average of about 400 Cs clocks.

If changes in the environment have less effect on a Y clock, or the physical processes upon which it's based have less random variation, then in might be more stable. Stability can be determined relatively quickly, using the 3-cornered hat method. But with the scales at issue, it may take a considerable length of time comparing the Y clock to the official realization of time in order to determine its accuracy (or perhaps more properly, calibrate it to be accurate).

Mostly using GPS.

The claim was "allowing nearly the entire globe to receive an accurate time signal..."

Even with no path length variation, good luck determining the path length to any specific location to micrometers in order to correct for the delay. Good luck doing so even within 15 meters (50 ns).

Using long term averaging, one might get frequency accuracy close to the claim, but not time (unless you have a hydrogen maser, I suppose). GPS is the best global time time distribution system available. If you look at BIPM Circular T, even national time labs have a hard time tracking UTC within 100 ns over a month. So, if you get GPS time accurate to 50 ns, (which is base off UTC(USNO), you're doing well.

The other factor is that the time isn't actually known until after the fact - UTC is a weighted average. UTC(NIST), which is what's being broadcast, can differ by ~4e-8/s (~40 ns) from the actual time, a billion times worse than the claim.

The claim was "allowing nearly the entire globe to receive an accurate time signal..."

Even with no path length variation, good luck determining the path length to any specific location to micrometers in order to correct for the delay. Good luck doing so even within 15 meters (50 ns).

Using long term averaging, one might get frequency accuracy close to the claim, but not time (unless you have a hydrogen maser, I suppose). GPS is the best global time time distribution system available. If you look at BIPM Circular T, even national time labs have a hard time tracking UTC within 100 ns over a month. So, if you get GPS time accurate to 50 ns, (which is base off UTC(USNO), you're doing well.

The other factor is that the time isn't actually known until after the fact - UTC is a weighted average. UTC(NIST), which is what's being broadcast, can differ by ~4e-8/s (~40 ns) from the actual time, a billion times worse than the claim.

Not really. Many jurisdictions (including the US) define UTC to be the legal time scale. Although it ticks at the same rate as TAI, it is different. Based on the widespread popular and legal use of UTC, it's more correct to say that TAI is UTC without leap seconds than to say that UTC is TAI with them. Physical realizations are generally referenced as UTC, not TAI (e.g. UTC(NIST), UTC(NPL)).

If you use TAI or UTC, you can never know what time is is right now, because it's only known after the fact - being based on the weighted average of an international collection of Cs clocks. "After the fact," meaning it may be up to a month before knowing what time it was, using BIPM Circular T. They are experimenting with a rapid update process (UTCr).

Then there's UT0, UT1 and UT2, which have no relationship with TAI at all, along with some national lab atomic time scales which are independent of TAI (e.g. TA(NIST), TA(CH) ).

The mass of such things has only been determined experimentally with a relatively significant margin of error. It's also not a definition that would lend itself to the development of practical realisations of the kilogram as what's called a transfer standard, nor a scale with which to test them.

It needs to be possible for weights to be produced, and then tested. The results from these tests would identify a given weight as being 1 kg plus or minus a measured error range. This then becomes a transfer standard, that can be used to calibrate other scales, and forms part of the traceability chain for certification. With a new definition, the current IPK would then become just another transfer standard along with all the other official copies.

You can read all about the new kg here...

except that BIPM, the providers of TAI, have published this http://www.bipm.org/cc/CCTF/Allowed/18/CCTF_09-27_note_on_UTC-ITU-R.pdf wherein the CCTF "stresses that TAI is the uniform time scale underlying UTC, and that it should not be considered as an alternative time reference." This appears to indicate that the CCTF and BIPM are not comfortable with the notion that operational systems might be employing TAI as their time scale. At the end of that paper they also discuss the possibility that TAI could cease to exist.

what about the metric time system?

We are using the metric time system. Under Chapter 4 Section 6, days, hours, and minutes are acceptable units using the customary definitions.

"How can a new method be more accurate than the method we use to define time?"

Because the current definition, based on a hyperfine transition of electrons in the Cesium atom, cannot be practically realized. The "definition refers to a caesium atom at rest at a temperature of 0 K." Neither of those conditions can be realized in the real world (there's gravity, and electromagnetic fields, etc.), and corrections are imperfect.

The new method discussed in the article, allows one to realize a better performing timebase. There are already ones which perform better, but the definition of the second hasn't changed.

The SI unit that equals 1000kg is a tonne. But the United States, in a fit of parochialism, has decided to rename it a "metric ton".

The SI unit that equals 1000 Kg is a megagram (Mg, or 10^6 grams). The tonne is not an SI unit, but, in a fit of nostalgia, has been metricized and accepted for use with the SI system.

See CCTF/09-27 which was submitted to ITU-R SG7A in 2007-09 and which said
                In the case of a redefinition of UTC without leap seconds, the
                CCTF would consider discussing the possibility of suppressing
                TAI, as it would remain parallel to the continuous UTC.
That makes it unclear whether the time scale known as TAI will continue to exist.

No, we don't have this option. See CCTF/09-27 which was submitted to ITU-R SG7A in 2007-09 and which said

That's not their call. TAI a well known and well-defined time scale. Unless and until we become subject to the Digital Millennium Timekeeping Act or some similar insanity, we have the option to use it however we please.

No, we don't have this option. See CCTF/09-27 which was submitted to ITU-R SG7A in 2007-09 and which said
                The CCTF realizes that some misunderstanding exists regarding
                the scope of application of the various time scales. It
                stresses that TAI is the uniform time scale underlying UTC,
                and that it should not be considered as an alternative time
                reference.

Isn't a second defined to be 1/60th of a minute which is 1/60th of an hour, which is 1/24th of a day? And a day is the amount of time it takes for the sun to revolve around the earth. For this reason, it won't add up at all since this change will have redefined what a second is.

No, a second is defined as:

The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.

Source.

Are you saying my definitions of voltage, current and resistance are somehow invalid?

Those definitions have actually changed over time, and may change further in the future.
"that as a result of recent advances, there are significant implications for, and potential benefits from, redefinitions of the kilogram, the ampere, the kelvin and the mole"
Just because something works, doesn't mean it's true. For example the Ptolemaic model of the solar system was pretty good at predicting the motion of the planets, but has since been shown as incorrect.

Uh, yes it was, in the 17th general conference of the International Committee for Weights and Measures.

http://www.bipm.org/en/CGPM/db/17/2/

Yes, NIST is just following up on an international proposal. The Comite International des Poids et Mesures in 2005 already proposed replacing the kilogram mass with something else.

There's already a system.

See http://www.bipm.org/en/CGPM/db/19/4/ "The names zepto and zetta are derived from septo suggesting the number seven (the seventh power of 10^3) and the letter "z" is substituted for the letter "s" to avoid the duplicate use of the letter "s" as a symbol. The names yocto and yotta are derived from octo, suggesting the number eight (the eight power of 10^3); the letter "y" is added to avoid the use of the letter "o" as a symbol because it may be confused with the number zero."

Also, the order is Z, Y, so the next is X. Hence the next prefix is likely to be xona

http://www.mindspring.com/~jimvb/unitsystem.htm

Other non-SI units, such as the units of time and angle, are so deeply embedded in the history and culture of the human race that they will continue to be used for the foreseeable future.

No, it doesn't... http://www.bipm.org/en/si/si_brochure/chapter3/prefixes.html

Note the link at the bottom to the IEC standard, and the fact that there is no exception listed.

Until recently kilo = 10^3 except for one easy-to-remember exception: a kilobyte was 2^10 bytes and similar for mega. Then the marketing departments at hard drive companies decided that they could provide 5% less space by calling a MB 10^6 bytes instead of 2^20 bytes. Before then, everyone knew that a kb was 1024 bytes. Now people don't know for sure. (For example, my computer reports that I have (and is sold as having) 2GB of RAM and a 250GB hard drive, but I'm pretty sure my RAM is actually in base 2. Is the 10MB attachment limit in base 2 or base 10? In other words, now that we've all gotten used to a kb being 1024 bytes, why are we changing it?

Would an exception saying 1kb = 2^10 bytes etc. be too complicated? Other SI rules and their exceptions: Prefixes for exponential factors greater than 0 are capitalized, except for deca, hecto, and kilo. Don't capitalize symbols for units unless the unit is named after a person, except for the liter (L).* Put spaces between the number and the symbol, except for %, degrees, arcminutes and arcseconds.*

Not to mention various ways of spelling liter/litre, country-specific abbreviations (amps), and country specific plurals (Henries), and it's ok to still use Celcius even though the SI unit is Kelvin.

*Liters, degrees, arcminutes, and arcseconds aren't really SI, and are on a separate list of non-SI units that are ok to use with SI.

Anyway, the International Bureau of Weights and Measures, in their22nd General Conference, decided that:

"the dot (point on the line) [is used] as the decimal marker in all the English language versions of its publications, including the English text of the SI Brochure (the definitive international reference on the SI), with the comma (on the line) remaining the decimal marker in all of its French language publications"

And from the 7th General Conference which was held in 1948:

"Numbers may be divided in groups of three in order to facilitate reading; neither dots nor commas are ever inserted in the spaces between groups."

Those familiar with scientific publications will also not that those recommandations are enforced by editors, even american ones, because those aim an international audience. Now, you do what you want inside your country.

Anyway, the International Bureau of Weights and Measures, in their22nd General Conference, decided that:

"the dot (point on the line) [is used] as the decimal marker in all the English language versions of its publications, including the English text of the SI Brochure (the definitive international reference on the SI), with the comma (on the line) remaining the decimal marker in all of its French language publications"

And from the 7th General Conference which was held in 1948:

"Numbers may be divided in groups of three in order to facilitate reading; neither dots nor commas are ever inserted in the spaces between groups."

Those familiar with scientific publications will also not that those recommandations are enforced by editors, even american ones, because those aim an international audience. Now, you do what you want inside your country.

If you are talking about the SI units, then the correct unit for an angle would actually be radian.

Regarding the angle and time measurements, although technically they are not part of the SI proper, they've been grandfathered in.

ms is not an SI unit. Seconds (s) are an SI unit. Prefixing it with the abbreviation of 'milli' is not the standard usage. Rather, you should append x10^-3 to the value before the unit.

While it's not a unit it's perfectly legal to prefix it with the abreviation (the prefix, actually) of milli. There really is an ambiguity there.

I can't see where anyone in this thread has said otherwise, nor am I aware of any attempts to redefine "Giga" as an SI prefix to mean anything else.

You're unaware that GB means 10^9 bytes while others think it should mean 2^30 bytes? In all cases, the giga- or G prefix means 10^9, while the gibi- or Gi prefix should be used for 2^30. http://en.wikipedia.org/wiki/Binary_prefix

(If you mean as in Gigabyte, then that's a completely different issue, since byte is not an SI unit. Unfortunately we are fighting against recent attempts to hijack it to a new and wrong numerical definition, simply to make it the same as the usage for SI units.)

It's not a different issue, according to NIST, IEC, NBS, IUPAC, and others. The issue has nothing to do with whether the unit being prefixed is SI or not, and everything to do with avoiding ambiguity (what about giga-dollars, for instance). Actually, the instance of megabytes and so forth is explicitly and clearly covered by the standards authorities. From the abovementioned wiki page: "Under this recommendation, the SI prefixes should only be used in the decimal sense: kilobyte and megabyte denote one thousand bytes and one million bytes respectively, while kibibyte and mebibyte denote 1,024 bytes and 1,048,576 bytes respectively. This recommendation has since been adopted by some other leading national and international standards, which now state that the prefixes k, M and G should always refer to powers of ten, even in the context of information technology." You can look up the SI definitions in French and English at http://www1.bipm.org/utils/common/pdf/si_brochure_8.pdf or if you're willing to pay, you can get IEEE 260.1-2004 which standardized kibi- gibi- and so forth. The "for idiots" summary is available from NIST http://physics.nist.gov/cuu/Units/binary.html

So disk drive manufacturers and others using GB to mean 10^9 bytes are actually correct. Those howling that it should mean 2^30 bytes are actually wrong. In every case.

24 hour time? How silly. That's not metric at all.

True, it is not strictly metric, but it does fall into the acceptable use standards.

So, Kelvin and Celsius are roughly the same scale

Roughly? how about, they *are* the same scale, just transposed 273.15 [units]
http://www.bipm.org/en/si/si_brochure/chapter2/2-2/table3.html

Nice try, but the SI standard is defined by the BIPM, not NIST. The SI base and derived units do not include bits or bytes.

Redefining the prefixes for base-2 units (e.g. byte) as base-10 does no one any good, as all the historical literature on the subject is already using the existing prefixes as base-2. The new terms (KiB/MiB/TiB) are clear enough, but the old ones -- which used to be unambiguous in context -- now have two possible meanings. Given the ridiculous names suggested for the new prefixes, that isn't going to change any time soon.

Anyway, it makes no sense to pile a base-10 prefix on top of a base-2 multiple of the base unit (one bit). It's like measuring distance in kilofeet, or area in millihectares. If you want base-10 units just use bits, and leave our perfectly useful binary prefixes well enough alone.

Nice try, but the SI standard is defined by the BIPM, not NIST. The SI base and derived units do not include bits or bytes.

Redefining the prefixes for base-2 units (e.g. byte) as base-10 does no one any good, as all the historical literature on the subject is already using the existing prefixes as base-2. The new terms (KiB/MiB/TiB) are clear enough, but the old ones -- which used to be unambiguous in context -- now have two possible meanings. Given the ridiculous names suggested for the new prefixes, that isn't going to change any time soon.

Anyway, it makes no sense to pile a base-10 prefix on top of a base-2 multiple of the base unit (one bit). It's like measuring distance in kilofeet, or area in millihectares. If you want base-10 units just use bits, and leave our perfectly useful binary prefixes well enough alone.

Since you are using hex, why one comma every 3 hex "figures"?

The grouping by 3 digits is actually an international standard adopted in 1948, at the 9th General Conference on Weights and Measures, although in fact my use of commas for the grouping is wrong: strictly speaking both the comma and point are reserved for the fractional separator only, and grouping should be done by empty spaces. Of course, this would make cut and paste very frustrating :)

Ahem! An hour is an acceptable SI unit of time.

I could claim that I was born before the 13th General Conference on Weights and Measures and exhort you to get off my lawn...but I'd be lying.

You guys mod this funny, but it's a little known fact that the terabyte was actually named after Tera Patrick in deference to her online body of work.

You must be joking.

When Resolution 6 was accepted, she was sixteen years from being born...

http://www.bipm.org/jsp/en/ViewCGPMResolution.jsp?CGPM=11&RES=12

This page probably explains it better than I can.

You're really measuring the force, by measuring the current required to balance a mass.

0 degrees C is defined as 273.15 degrees K (exactly). People usually round down the .15 because it's more sig figs than they really need. Technically that means it's -99.67 degrees F.

Because the joule is almost worthless as an everyday measure of household energy usage. You know the wattage of a device. You want to know how much total power you've used. The natural measure, then, is to say that I've used 100 watts for ten hours, so I've used 1000 watt-hours. The unit just fits. Multiply watts times hours. This unit is extremely easy to use.

A joule, by contrast, is horrible to the point of being nearly useless for this purpose. A joule is equal to a watt-second. Unless you are turning on and off lights every few seconds, you don't want to try to think about your power usage in terms of the number of seconds a device was on. You also won't want to think of thousands (kilojoules) or millions (megajoules) of seconds, either, because our clocks are not divided into thousand or million second increments. This unit is horribly cumbersome to use, at least for the purpose of measuring household electrical usage.

It is MUCH easier to think about power utilization in terms of a larger time unit such as hours, as it is a more meaningful time interval when dealing with large values of time. Since we're not going to change the number of seconds in an hour, it just makes a lot more sense to use hours as the base unit of measurement when it is appropriate rather than multiplying by 3600 to try to force things into a per-second frame of reference. Measuring typical spans of human life in seconds is just silly.

For this reason, the U.S. (and most of the world, AFAIK) uses the kWh as a unit of electrical power utilization for metering purposes. Oh, and the BIPM does recognize the hour as a non-SI unit acceptable for use with SI units, making the watt-hour de facto acceptable.

The kilogram doesn't define the concept of mass, it merely measures it (imperfectly). Same with the Newton and the concept of force. Thus the force of the Earth's gravity on the Kilogram is qualitatively different, even if our imperfect measurements are incapable of quantifying it.

You're going to have a very hard time explaining how the latter logically follows from the former (justifying your use of "thus" above). You might want to go the route of saying that Newton's Law of Universal Gravitation applies, but there's no logical reason to think that the process that affected the prototype didn't affect the rest of the planet as well.

From the SI: "The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram." Note that the prototype kilogram has mass of exactly, to infinite precision, 1.0... kg by definition.

Mass is conceptually understood as the quantity of matter in an object or system. If the prototype kilogram contains less matter now than before, either the kilogram is not a measure of mass, or mass is fundamentally misunderstood.

By the way, in the sense of "taking a measurement", the kilogram does not measure mass. Scales or accelerometers do. This is an important distinction. Don't conflate the notions.

Add to this that recently scientists have discovered how to "slow down" light

Gosh, I'm usually very mild-mannered when it comes to /., but sorry, this is a load of steaming crap. "Recently discovered"? Do you even you know what you're talking about? Does the term 'refraction' mean nothing to you?

According to Wikipedia, "the second is currently defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

Sigh. Not according to Wikipedia, friend, but according to the Systeme Internationale . Wikipedia merely quotes SI's definition; it doesn't do the defining by itself. There's a difference.

IEC doesn't define the metric standard. BIPM/SI does.

Actually it is mole, "mol" is the standard abbreviation. BIPM - mole