What is the standard for pressure?

Discussion in 'Physics' started by #12, Jan 13, 2016.

  1. #12

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  2. WBahn

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    I recall that discussion, though not all that well. What I recall is disagreeing with the notion that saying that something is "the gold standard" is the same as saying that it is THE official, defining standard. In particular, the height of a column of mercury is NOT the definition of pressure, specifically because the pressure of a column of mercury of a given height varies with several parameters such as temperature, altitude, and latitude (not to mention variations in the local gravitational constant due to the local makeup of the Earth itself and further not to mention the HUGE differences that result if you are on a different planet/moon or in orbit). A "gold standard" is nothing more than an agreed upon "best reference practice" for a particular application and has no relation whatsoever to any legal or official standard of measurement. For taking external blood pressure measurements, using a mercury manometer is the agreed upon best practice given the accuracy and precision requirements of blood pressure measurements -- namely is it almost always safe to ignore these very real variations because they have effects that are less than the tolerance limits that are needed. But that in no way elevates mercury-based pressure measurements to the level of an official, legal defining standard for pressure. The legal and official definition of pressure is the force per unit area. Force is defined in terms of mass and acceleration. Acceleration is defined in terms of distance and time. Area is defined in terms of distance. Mass, distance, and time are fundamental constants that are arbitrarily defined (and periodically redefined) by international standards-setting committees.

    But this all seems well adrift from this thread's focus, so let's take this discussion elsewhere if we want to revive it.
     
  3. #12

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    That is where we disagree. I can't find it right now, but some committee declared the mercury sphygmomanometer to be the OFFICIAL defining standard. IIRC is was in 1881.

    The webpage has a line drawing of a bunch of stuffy old men at the top and tells about a meeting to declare standards. When the stuffy old men say it's the Gold Standard, that makes it Official as far as I can tell.

    So you spend your time and brain power arguing that just because an international meeting on weights and measures calls the mercury sphygmomanometer, "The Gold Standard", does that really, really, make it, "Official". And I think, "Why don't you go count the atoms in your atomic clock?" How picky can you be that a conference on weights and measures isn't Official enough for you? Do you doubt that there are really, Officially, 25.4 millimeters in an inch? That was declared Official in the same way.
     
    Last edited: Jan 14, 2016
  4. WBahn

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    Okay -- for argument's sake let's stipulate that some official committee with standing to make legal measurement standards made it the official defining standard of pressure in 1881. I can guarantee that it is NOT the standard of pressure today and hasn't been for over half a century since the publishing of the SI standards in 1960. Even before that, the MKS system, upon which SI is primarily based) was proposed in 1901 and widely adopted over the next decade or so. Hanging your hat on a definition that is no longer in force is nor more valid then someone pointing to an even prior definition of something and claiming that IT is the definition instead. Go that route and we end up with someone asserting that the definition of an inch is NOT 2.54 cm but rather three grains of barley, dry and round, placed end to end, lengthwise.
     
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  5. cmartinez

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    This thread has just earned my undivided attention... I'm a big advocate for the metric system, but then again, I'm willing to consider the authority of those whose credentials I respect.
    In my opinion, a consistent definition of units should defined by an aristocratic-democracy. That is, it should be the consensus of those whose education is well above the average college graduate. Deep down, any system of units is an attempt at a human communication standard, after all.
     
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  6. #12

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    I am sure that the Standards in 1881 were abysmal compared to the Standards in 1981. I don't even know if the mercury sphygmomanometer was declared to be The Gold Standard at Standard Temperature and Pressure because I don't know whether STP had been defined in 1881. You took me to task about the validity of the standard I mentioned and I provided four verifications from four different medical dictionaries. I think from your answer that you still consider it a matter of speculation as to whether that Standard is really, "Official". Any time you can point to a more modern Gold Standard for blood pressure measurement, I will use that Standard. The same goes for millimeters in an inch and resistance in an Ohm.

    What I will not do is try to prove what is, "Official" enough for you. After providing quotations and links to four different sources and not convincing you of anything, I don't believe I have the power to prove what is Official enough for you.

    I wasn't on the committees. I didn't declare the Standards. I don't have to defend them, or justify them, or prove to you that they are, "Official". I am going to use Standards and Conventions which were declared by international committees. Everybody else is too. If they aren't, "Official" enough for you, point to one that is. Some people might not believe your reference is, "Official" but at least you will be pointing to an actual, verifiable, publicly known reference, instead of asking uncredentialed people on the Internet to prove something is Official enough for you.
     
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  7. profbuxton

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    As an aside, wasn't the STANDARD for lengths taken from the English kings arm length. An inch was the length of a barleycorn etc. And the english mile was different in most counties, as was the time.
     
  8. boatsman

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    The standard foot was taken, I believe, from the length of Henry VIII's foot or possibly from the size of another of his appendages considering he was married six times.
     
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  9. Papabravo

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    He was married six time because he was the KING. Also he never consummated marriage number four to Anne of Cleves. It was good to be the king in those days.
     
  10. boatsman

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    Reminds me of the old joke: Once a king, always a king. Once a knight, dead at forty!
     
  11. #12

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    That's my opinion of a great way to die.:p Unfortunately, I missed that opportunity.:(
    I would like to ask whether you are in competition with, or in collusion with, joeyd999 in the goal of posting the highest number of sexually oriented references.
     
  12. joeyd999

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    Really? I thought my references were quite mild considering many others that made even me cringe.
     
  13. boatsman

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    Not really, joeyd999 is in a class on his own.
     
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  14. #12

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    I didn't say, "sexually perverted". I said, "sexually oriented". Big difference.
     
  15. cmartinez

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    Oh, I'm glad you clarify... I misread it as "sexually disoriented" at first...
     
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  16. JoeJester

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    Gold standards change upon further review of the new and more accurate definition.

    The lowly second ... it is NOT 1/60th of a minute, by, and I'm getting political here, International Agreement.

    So depending on the field, time can be UTC, UT0. UT1, et al. Every now and then we get a leap second to bring UTC closer to UT1.
     
  17. cmartinez

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    Now that you mention it... I believe the standard for pressure is defined by how many days are left in a deadline before penalties take effect... :D
     
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  18. GopherT

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    It seems that people outside of this website disagree with you. I don't know if it is your definition of Gold Standard or your conclusion that a measurement technique used for years results in an answer that has been a basis for comparison across a huge population of technicians, geography and time. Whether or not it accounts for anomolies that you believe are important, or inconsistencies in the way technicians implement the method, it remains the "gold standard" - until a new gold standard (or gilded standard) displaces it.

    http://hyper.ahajournals.org/content/45/1/142.full
    The gold standard for clinical blood pressure measurement has always been readings taken by a trained health care provider using a mercury sphygmomanometer and the Korotkoff sound technique, but there is increasing evidence that this procedure may lead to the misclassification of large numbers of individuals as hypertensive and also to a failure to diagnose blood pressure that may be normal in the clinic setting but elevated at other times in some individuals. There are 3 main reasons for this: (1) inaccuracies in the methods, some of which are avoidable; (2) the inherent variability of blood pressure; and (3) the tendency for blood pressure to increase in the presence of a physician (the so-called white coat effect).

    Even gold standards are not perfect or even the best. Webster give an example sentence using Gold Standard and they have not selected the best option, just a popular and commonly accepted option.
    "the gold standard for accurate experimental procedures is the double-blind medication trial"​
    When, in fact, a double, double-blind test method exists where patients getting the placebo are flipped and given the real API and results measured - to avoid the placebo effect.

    Also, there is a shop near my house that claims to be the Gold Standard in Pizza. I have not looked into their measurement protocols and use of SI units, but, I have no reason to doubt them.
     
    Last edited: Jan 15, 2016
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  19. WBahn

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    I'm having a hard time determining what your point is because you seem to be dancing on both sides. I've already addressed the issue of using the phrase "gold standard". It is just that -- a phrase -- and the appearance of the word "standard" in it is immaterial. It's merely a phrase borrowed from the field of economics. It is most commonly used as a pseudo-official term within the medical field, but is widely used colloquially elsewhere. Even in the medical field the use of that particular term is deprecated in favor of "criterion standard" or "clinical definition" (the two phrases aren't quite the same thing" in many/most clinical publications.

    Keep in mind that the question at hand is not whether the use of a mercury manometer is the "gold standard" for taking blood pressure measurements. That is entirely beside the point. The question is whether the concept of "pressure" is defined via a mercury manometer. IIRC, in the original discussion is was claimed that whatever air pressure was indicated by a mercury manometer WAS the true air pressure because a mercury manometer was how pressure was defined.
     
  20. #12

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    Air pressure is also measured in units called, "inches of water column" and, "pounds per square inch". Either of those measurements can be performed directly by a mechanical apparatus. The water column method is very similar to the, "millimeters of mercury" method, but more convenient for rather small amounts of pressure difference. An apparatus for measuring directly in pounds per square inch is a lot more inconvenient, but it can be done.

    So, of all these direct measurement techniques, why do you pick the mercury method as less valid?
    Do the millimeters of mercury not convert to inches of water column or pounds per square inch?
     
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