View source for Talk:Torr

{{WikiProject banner shell|class=C|vital=yes|1=
{{WikiProject Measurement|importance=mid}}
}}

== temperature and pressure ==
[[User:199.168.7.243|199.168.7.243]] 20:42, 13 August 2007 (UTC)The artilce introduces the Torr using this text:  It is the atmospheric pressure that supports a column of mercury 1 millimeter high. This wording is ambiguous as atmospheric pressure is ~760 torr, or ~760mmHg.  One Torr is the pressure that supports a column of mercury 1 millimeter high.  It is most often used to measure gas pressures including atmospheric pressures.

[[User:199.168.7.243|199.168.7.243]] 20:42, 13 August 2007 (UTC)

Presumably this is 1 mmHg at standard temperature and pressure?

==Numeric Notation==
Can we stick to either Engineering Notation or normalized Scientific Notation (or even plain decimal)?
For example in the conversion table, in the atm column, it has 1.0197×10<sup>−5</sup> in one row and 70.307×10<sup>−3</sup> in another.  It seems like consistently using normalized Scientific Notation (i.e., changing the latter to 7.0307×10<sup>−2</sup>) would make it a lot easier to get a quick sense of the different magnitudes.[[User:Erikmartin|Erikmartin]] ([[User talk:Erikmartin|talk]]) 18:28, 22 October 2008 (UTC)

==Band?==

I eliminated this: 

'''The Torr' is also the name given to a Bristol based rock band which formed in 1998 and are still performing and recording today. Noteable members include: Jon Steadman, Neil Berry & James Trotham.''

If it is found useful, it should be put in a stub page or in a disambiguation page. [[User:SaintCahier|SaintCahier]] 17:00, 6 August 2007 (UTC)

==More importantly, 1mmHG at Earth's gravity == 

Is there an official torr now defined in terms of another measurement system, or do you measure your own?

:This is close to 1 mmHg at 0 °C and standard gravity.  That is the temperature that was most often used for metric units based on a column of mercury; for inches of mercury, in earlier times 60 °F was more common but the ones still in use today are most often exactly equal to 24.4 mmHg, so are also essentially equivalent to the 32 °F (0 °C) variety, though mercury is no longer actually used in the precise definitions.

:It's just that defining a standard atmosphere as both 101.325 kPa and 760 mmHg makes a more precise definition of these units based on the units for which standards are currently maintained, namely the SI units.  That 101.325 kPa number was chosen because it was, to the nearest pascal, the calculated pressure of 760 mm mercury at a certain conventional density under those conditions.  [[User:Gene Nygaard|Gene Nygaard]] 22:22, 20 Dec 2004 (UTC)

At no stage have we heard which authority originally defined the Torr, nor which international authority currently owns / maintains the definition.  The arguments between AMA vs NIST are parochial for the international readership, unless one of these turns out to be the internationally-recognised authority for the definition.  While millimetre of mercury may be a non-SI unit, the 'millimeter' spelling is sanctioned by the US Government.  The SI English spelling is millimetre.  [[User:Icairns|Ian Cairns]] 22:49, 24 Jan 2005 (UTC)

#Where did you get the silly notion that some one body must "own" each unit of measure?
#There is no rule that any international body must act.
#There is no international body with plenary authority in this area.
#There can be and are disagreements among various international standards setting agencies, just as there are differences between the AMA Style Guide and the NIST Style Guide concerning the symbol for millimeters of mercury.
#There is no "SI English spelling."  The BIPM chooses to follow use one spelling in their work; they do not state it as a general rule.  Do you understand the difference?  That's a "house rule", not a prescription.
: &mdash; [[User:Gene Nygaard|Gene Nygaard]] 23:41, 24 Jan 2005 (UTC)


:Most relevant to this discussion is that we at Wikipedia have our own "house rules"&mdash; and one of them is that you do not arbitrarily mess with an article's consistent use of a particular spelling of litre/liter, color/colour, tyre/tire, and the like.  [[User:Gene Nygaard|Gene Nygaard]] 23:50, 24 Jan 2005 (UTC)

:Another point:  There are lots of [[Canadian Tire]] stores, and not one [[Canadian Tyre]] store.  We also spell this word ''tire'' in the United States, so this is an ''international English spelling''.  Yet there are Wikipedia articles which spell this word ''tyre''. International does not mean prescriptive for the whole English-speaking world. [[User:Gene Nygaard|Gene Nygaard]] 00:55, 25 Jan 2005 (UTC)

==Nonexistent distinction==

I reverted this addition by [[User:Urhixidur]]:
*Strictly speaking, the millimetre of mercury and the torr are slighly different units.  Using the conventional density of mercury [http://home.att.net/~numericana/answer/constants.htm] of 13595.1 kg/m<sup>3</sup> and the conventional acceleration of gravity, 760 mmHg equals a pressure of exactly 101,325.0144354 Pa, which was rounded down in [[1954]] by the 10th [[CGPM]] to give the conventional value of the atmosphere (101,325 Pa).  The torr, defined as 1/760 of the latter value, is thus slightly smaller than the mmHg (by about 0.14 ppm), although both are used interchangeably in practice.

These are merely successive definitons of the same unit.  Nobody redefining this unit has ever intended for there to coexist two slightly different variations of the unit.  A particular name may be deprecated, but I'm not sure that that is the case either.  [[User:Gene Nygaard|Gene Nygaard]] 15:30, 26 Jun 2005 (UTC)

:I wish Gene were right, but he isn't.  As [http://www.sizes.com/units/mmHg.htm this source] and [http://www.npl.co.uk/pressure/punits.html this other source] show, the mmHg used to be defined (by the World Meteorological Organization, according to [http://stommel.tamu.edu/~baum/paleo/paleogloss-old/node38.html this]) as I described in the excerpt above.  We're agreed that there was never an intent to have the torr actually different from the mmHg, but in practice they were (and still are) because the definitions disagreed.  This point is worth making, if only for the historical insight into metrology it provides.
:[[User:Urhixidur|Urhixidur]] 2005 June 28 12:48 (UTC)

::Your first source does not say when WMO defined the mmHg this way, and is not an indication that this is not just a successive definitions problem.  Whether or not the WMO has ever formally adopted an updated version is irrelevant to the question, especially when the difference is about four decimal orders of magnitude removed from making a difference in any of these measurements as made in anything in the province of the WMO.  And especially since the WMO never uses them any more, except perhaps dealings with the U.S. NWS which uses them yet in public and aviation weather reports, though not in the more "scientific" contexts.   Your second source may be an indication of some remaining unresolved inconsistency in [[British Standard]]s (and once again, likely mostly irrelevant for the purposes for which those definitions are used), still not anything to disprove a successive refinement of the definition of a unit of measure quite legitimately and properly known by both names under both definitions (even if very specific legalistic applications might require one form or the other in some particular context).  

::The thing is, as even your arguments point out so well, nobody has plenary authority in this regard.  And nobody is required to make these definitions, or to update them immmediately even if a de facto standard becomes established which varies slightly from them.  There is nothing improper about one group of users deciding to use the name "millimetre of mercury" and with another group using the name "torr" to refer to the unit defined by saying that a standard atmosphere is equal to both 760 of that unit and to 101.325 kPa, and there is nothing improper about one group of users deciding to use "millimetre of mercury" and with another group using "torr" to refer to the unit defined by saying that this refers to the pressure exerted by mercury at a certain temperature and at a certain acceleration of gravity, and there is nothing improper about one group of users deciding to use "millimetre of mercury" and with another group using "torr" to refer to the unit defined by making that definition less ambiguous by specifying a specific density and a specific acceleration of free fall. 

But what we do know or at least can determine is the historical progression of those definitions:  The middle of those three first, then the last one, then the first one.  There is nothing improper with various groups of people choosing to use "millimeter of mercury" and "torr" as exact synonyms under any of these definitions.  [[User:Gene Nygaard|Gene Nygaard]] 28 June 2005 15:03 (UTC)

:Not to reopen the debate on differences in the size or derivation of one mmHg vs one Torr, but [http://www.dekkervacuum.com/reference/technical.htm this page] suggests that Torr are an absolute value, starting with zero Torr at a perfect vacuum, while mmHg indicate a gauge pressure.  Admittedly, this is from a manufacturer, not a scientific body, but it still seems worth discussing here, if not on the actual page.  Anyone?  --[[User:Badger151|Badger151]] 03:58, 26 July 2006 (UTC)

==Conversion tables==

The following table of conversion factors appears in many Wikipedia articles:

{{Pressure Units}}


The table was removed from the present article because it ''flatly contradicts'' the article itself.  The table says that 1 Torr = 1 mmHg.  One of the main points of the article is that 1 Torr is ''not'' equal to1 mmHg. While it is true that 1 Torr ''almost'' equals 1 mmHg, the two units are ''not'' identical.  

Among the many articles in Wikipedia that deal with pressure, some contain copies of this table while others do not.  An example of the former is [[Pressure]].  An example of the latter is  [[Conversion of units]].  Since the table is, at best, misleading (and frankly ''wrong'' from a technical viewpoint), I think it should be ''entirely'' removed from Wikipedia (not just from the present article).  Also, as a matter of principle, “millimeter of mercury” and “mmHg” should not be redirected to [[Torr]].

:The table you pasted here says that 1 torr ≈ 1 mm Hg; that's "approximately equal".  Maybe your browser doesn't support unicode properly? --[[User:Slashme|Slashme]] 09:16, 28 October 2007 (UTC)

::It should be "equals".  See the section above this.  Just like feet or meters or whatever, these units have had various definitions over time.  That's all that is involved here.  -- [[User:Gene Nygaard|Gene Nygaard]] ([[User talk:Gene Nygaard|talk]]) 17:16, 16 November 2007 (UTC)

==Conversion of SI pressure units==

The SI unit of pressure is the pascal (Pa).  Other units in common use are derived from SI units according to the following four definitions (see article for references):
	
*   The ''atmosphere'' (symbol: atm) is defined as exactly 101,325 Pa. 
*   The ''bar'' (symbol: bar) is defined as exactly 100,000 Pa. 
*    The ''torr'' (symbol: Torr) is defined as exactly 1/760 atm.
*    The ''millimeter of mercury'' (symbol: mmHg) is defined as the product of (1) the “standard’ density of mercury at 0 °C (13.5951 g/cm<sup>3</sup>) and (2) the “standard” acceleration of gravity g<sub>n</sub> (9.80665 m/s<sup>2</sup>).

From these four definitions, the entire conversion table can be constructed.  In the tables shown below, I omit conversions involving the ''pound-force per square inch'' (a non-SI unit) and the ''technical atmosphere'' (an obsolete unit involving the avoirdupois ''kilogram-force'').  There is nothing wrong with having these units in a conversion table; they are omitted here only because we are discussing SI units.

The first table shows ''exact'' conversion factors.  This format emphasizes the underlying simplicity of the SI, and shows clearly why the conversion factors for Torr and mmHg are different:[[Image:Pressure_Conversion_(Exact).png|center|600px]]

The second table gives ''approximate'' conversion factors (to six significant figures).  This is the format that is used in practice.  The torr and the millimeter of mercury are so similar that their differences do not appear at six significant figures.  Note the pairs of identical values scattered throughout the table:[[Image:Pressure_Conversion_(6-place).png|center|600px]]

The differences become apparent when additional significant figures are included:

          1 Pa = 0.00750061'''68271''' Torr                           1 bar = 750.061'''68271''' Torr  
               = 0.00750061'''57585''' mmHg                                 = 750.061'''57585''' mmHg

          1 atm = 760.00000000  Torr                            1 Torr = 0.999999'''85753''' mmHg
                = 759.999'''89173'''  mmHg                            1 mmHg = 1.000000'''14247''' Torr

          1 Torr = 0.001333223'''68421''' bar                         1 Torr = 133.3223'''68421''' Pa
          1 mmHg = 0.001333223'''87415''' bar ('''exactly''' )              1 mmHg = 133.3223'''87415''' Pa ('''exactly''')

With two exceptions (noted above) these decimal conversion factors are infinitely long.  The two exceptions are ''exact'' conversion factors in decimal form.  Of course, ''all'' of the fractions in the first table are exact conversion factors.

Clearly, these distinctions are so small as to be negligible for most purposes.  However, scientific articles in Wikipedia should not tolerate ambiguities, especially when thy are misleading.
[[User:Btarski|Btarski]] 23:12, 3 October 2007 (UTC)

==The cgs system==

The statement that the torr “was used in the cgs system of units” is incorrect.  The [[cgs]] unit of pressure was the ''dyne per square centimeter''.  It was called the ''[[barye]],'' equal to 0.1 Pa.<ref>The Wikipedia article on the [[cgs]] system shows the torr and the barye as synonymous, which is incorrect.</ref> 

The torr was used in conjunction with both the ''cgs'' and the ''mks'' systems.  It was usually taken to mean “millimeter of mercury,” but it was also used to mean 1/760 of a standard atmosphere.  As discussed in the article, these two definitions are ''incompatible''.

When the ''standard atmosphere'' was defined as exactly 101325 Pa <ref>In 1954; see article for reference.  Note that the standard atmosphere was originally defined in cgs units (1 atm =  1013250 ''barye'' = 1013250 ''newton-meters per square centimeter'').  The definition of the standard atmosphere (1954) preceded the adoption of the SI (1960).</ref> the torr was defined to make 1 atm = 760 torr. The millimeter of mercury was never a part of the cgs, mks or SI systems.
 
The cgs system is now ''obsolete''.  Any discussion of the torr in relation to the cgs system is of historical interest only. 

Unlike the mmHg, the torr (with its modern definition of 1/760 1 atm = 101325/760 Pa) is a perfectly legitimate unit of pressure, derived from SI units.  Its use in general is discouraged, <ref>http://physics.nist.gov/Pubs/SP811/sec05.html</ref>since the SI unit of pressure is the ''pascal''.

Various Wikipedia articles continue to confuse the matter by offering different interpretations of both the torr and the mmHg.  The articles on [[pressure]], [[bar (unit)]] and [[pascal (unit)]] all contain the ''incorrect'' conversion table discussed above (under “Conversion tables”).  This table (which treats the torr and the mmHg as identical) was correct until 1954.  It has been obsolete ever since then.   

<references/>
[[User:Btarski|Btarski]] 19:01, 9 October 2007 (UTC)

:You forgot to remove it from the category as well.  I'll take care of that.  -- [[User:Gene Nygaard|Gene Nygaard]] ([[User talk:Gene Nygaard|talk]]) 17:07, 16 November 2007 (UTC)

== Is Torr absolute? ==

Here's a question that I've struggled with when I first started dealing with vacuum measurements. Without bringing pascals into this, torr is often stated as being equal to mmHg. On most gauges and conversion tables, mmHg is not an absolute measurement, that is, 0 mmHg = air pressure and 760 mmHg = total vacuum. I've been told by more than a few flashlamp manufacturers that Torr is equal to mmHg(absolute), that is, 0 torr = total vacuum and 760 torr = air pressure. To quote from correspondence I had with one expert "what? 730 is more [pressure] than 100 or 500. Is there a typo here?" If torr is an absolute measurement and mmHg is not, (like the difference between Celsius and Kelvin), I think this distinction should be made clearer in the article. [[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 00:39, 26 November 2008 (UTC)
Is there anyone here who can answr this question?[[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 20:05, 12 January 2009 (UTC)

:Sure.  The answer is no.  The "torr" and the "millimeter of mercury" are totally interchangeable, in any of their definitions over time, and whether used to measure gauge pressure or absolute pressure.  [[User:Gene Nygaard|Gene Nygaard]] ([[User talk:Gene Nygaard|talk]]) 17:00, 6 February 2010 (UTC)

::Do you have a source for that. Here's why I ask. When building [[flashtube]]s, the pressure for xenon is usually around 500 Torr, whereas the pressure for krypton is usually around 760 Torr, although pressures can be as high as 3000 Torr or as low as 50. On guages they call it mmHg Absolute, but no "absolute" is listed after Torr. [[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 17:34, 6 February 2010 (UTC)

:::There's no accounting for everyone's ideosyncracies.  Rarely does anybody use both torr and millimeters of mercury; most people will use one name or the other for this unit, and will use the same name whether they are talking about absolute pressures or gauge pressures.  
::#Just go look at [[Special:WhatLinksHere/Torr]] and tally up how many times each name of this unit ([[mmHg]] and various other possibilities are on that list through their redirects) is used for an absolute pressure, and how many times that name of the unit is used for gauge pressure.  Or search the internet with your favorite search engine, and do the same.  
::#Find any Wikipedia articles (other than the ones about units of measure or systems of units) which use both "Torr" or "torrs" on the one hand, and "mmHg" or "mm Hg" or a spelled out version with either -er or -re spellings.  Tell us how each is used there, and whether or not both were added by the same editor.  [[User:Gene Nygaard|Gene Nygaard]] ([[User talk:Gene Nygaard|talk]]) 14:47, 7 February 2010 (UTC)

::::By the way, you can see a whole lot of nonsense on various gauges.  For example, see this one at [[File:WPGaugeFace.jpg]]  
:::::It is centered on one atmosphere of pressure, and it measures gauge pressure in either direction (no absolute pressures)
:::::*It measures negative gauge pressures in "CM/VAC" (i.e., cmHg) and it measures positive gauge pressures in "KG/CM²" (kgf/cm²)
:::::*It measures negative gauge pressures in "IN/VAC" (inHg) and it measures positive gauge pressures in "PSI" (lbf/in²)
:::::By your logic, should we say that "psi" are only used for gauge pressure? That "cmHg" are only used for gauge pressure?  I don't think so. [[User:Gene Nygaard|Gene Nygaard]] ([[User talk:Gene Nygaard|talk]]) 15:30, 7 February 2010 (UTC)

::::::One additional point:  we know that a pressure of a few micrometers of mercury or especially less than 1 µmHg are absolute pressure, and we know that pressures of a few millitorrs or less are absolute pressure.  We don't know that because of the units used, however.  We know that because that little difference from a pressure of about one atmosphere is unmeasurable.  Our gauges simply cannot show such a small difference as a gauge pressure.  [[User:Gene Nygaard|Gene Nygaard]] ([[User talk:Gene Nygaard|talk]]) 15:42, 7 February 2010 (UTC)

:::::::I apologize if my question has offended you. My only logic was to clear up some confusion which plagued me in my younger days. Thanks for your assistance. [[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 21:38, 7 February 2010 (UTC)

== typo? ==
On the first row, third column of the table, it says 1 Pa = 1x10^5, whereas in the comment underneath explaining how to read the table it says 1Pa=1x10^5. Which is correct?

[[User:Ganaren|Ganaren]] ([[User talk:Ganaren|talk]]) 01:52, 7 October 2009 (UTC)

== Dubious ==

"The torr, a more convenient unit for low pressures," it is claimed "is used in high-vacuum physics and engineering."

*Where's the citation?
*Who says it's "more convenient" (than what)?

[[User:Jimp|J<small>IM</small>p]]<sub>&nbsp;[[User talk:Jimp|talk]]·[[Special:Contributions/Jimp|cont]]</sub> 19:40, 23 August 2011 (UTC)

:I agree on the first sentence. That's an opinon, because what's convenient for one person may be a hassle for another. (Especially if you don't realize that in high vacuum physics, like plasma physics, the term "Torr" usually means "Torr (Absolute).) However, the fact that it is used quite often in things like plasma physics is pretty well known. I'll see if I can find a source for that. [[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 20:57, 23 August 2011 (UTC)

See [http://www.mksinst.com/product/category.aspx?CategoryID=35 MKS Instruments vacuum gauges] or [http://www.helixtechnology.com/products/category28.html Granville Phillips ion gauges (now owned by Helix Technology)].  I have personally gone to Granville Phillips location in Boulder, CO to pick up ion gauges I bought for high vacuum use.  I've also maintained ultra high vacuum systems for physics research and all the gauges read out in Torr.  Working as an engineer in the thin-film magnetic recording and MEMS industries the process specifications, production logs, and tooling all used Torr.
--[[User:NimbleThink|NimbleThink]] ([[User talk:NimbleThink|talk]]) 22:43, 30 January 2012 (UTC)

:Yeah, I started out as a hobbiest, making my own flashtubes for lasers. My first vacuum gauges read in mmHg, none of which were "absolute readings, (ie: 0 mmHg was equal to air pressure and 760 is total vacuum). It was a bit confusing as to what "500 Torr fill pressure" actually meant, until I began talking to flashtube manufacturers and experts, like Advanced Radiation and Don Klipstein. My first gauges that read in Torr came from Cole-Parmer, and those were all "absolute" readings, (ie: 0 Torr equals total vacuum and 760 is air pressure), whereas the mmHg guages they sold were not. I can see where, in the scientific community, "Torr" might be a convenient way to differentiate between the two, similar to the way "Kelvin" is a convenient way to differentiate between Celsius and Celsius (Absolute). However, I have never found a source that explains it in those terms. In the scentific community, this knowledge seems to be taken for granted. [[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 23:51, 30 January 2012 (UTC)
::
::Definitely torr is common in high vacuum physics and engineering. I suspect for no other reason than everyone else does it. Most often, what one wants is log(absolute pressure) to about 1 significant digit, or maybe 2. It is usually measured in torr to one significant digit, and (more important) the power of 10. Ion gauges measure absolute pressure, maybe to microtorr. For systems that are not high vacuum, including the backing pump for a diffusion pump, maybe millitorr with a thermocouple gauge. I suspect that the calibration of thermocouple guage depends on the gas. [[User:Gah4|Gah4]] ([[User talk:Gah4|talk]]) 21:15, 20 October 2022 (UTC)

:::It's practically essential to use an absolute scale in aeronautics and meteorology, because that's how an altimeter works. In my experience with deep vacuum measurements, a normal pressure gauge, like a Bourdon gauge or even a slack tube, will give you fluctuating readings due to the fluctuations in atmospheric pressure. It's like, if you take your blood pressure at sea level, it may read normal, but will be much, much higher if you take it on top of Mt. Everest. The absolute pressure is probably the same, but the backpressure provided by the atmosphere is much lower at high altitudes. People like Kelvin and Edison, who were pioneers in deep vacuum measurements, noticed this problem very early on, and it's around that time that they began using the term "torr" in deep vacuum studies. [[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 21:25, 20 October 2022 (UTC)

== When was word torr introduced? ==
It's the first time I hear about torr. Everyone around me is using mmHg. Is it some kind of new beurocratical initiative like with mho (1/ohm)? When was word torr suggested? Should I write 120/80 torr instead of 120/80 mmHg?  <small><span class="autosigned">— Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[User:Comecra|Comecra]] ([[User talk:Comecra|talk]] • [[Special:Contributions/Comecra|contribs]]) 12:37, 30 May 2012 (UTC)</span></small><!-- Template:Unsigned --> <!--Autosigned by SineBot-->

:Torr was named after Evangelista Torricelli, after he invented mmHg, in the early 1600s. For nearly all intents and purposes, torr is the same as mmHg. However, in most scientific journals, torr usually refers to mmHg (Absolute), (ie: 0 torr = total vacuum), whereas mmHg refers to non-absolute readings, (ie: 0 mmHg = air pressure = 760 torr. Likewise, total vacuum = -760 mmHg). So, 120/80 mmHg will usually equal 880/840 torr . I hope that helps. [[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 16:19, 30 May 2012 (UTC)
:If it helps, here is a definition from the book ''Exercise Physiology: Nutrition, Energy, and Human Performance'', which helps explain the difference between absolute and relative (barometric) pressures:
<blockquote>
'''The torr''' -- named after the Italian physicist and mathematician Evangelista Torricelli (1608--1647) who invented the barometer in 1644-- is not an SI unit but an expression of gas pressure. One torr equals the pressure necessary to raise a 1 mm column of mercury 1 mm high at 0°C against the standard acceleration of gravity at 45° north latitude (980.6 cm * s <sup>-2</sup>). One standard atmosphere equals 760 torr. The barometric reading varies with changing weather conditions and becomes lower with increasing altitude.
</blockquote>
:[[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 22:42, 30 May 2012 (UTC)
<blockquote>
Zaereth, thank you for your reply. Sometimes an established term is renamed to commemorate inventor. For example term rpm (revolutions per minure) was renamed into Herz in 20-th century (The name was established by the International Electrotechnical Commission (IEC) in 1930). I have never seen anyone referencing mmHg as torrs. When was the word torr suggested?
[[User:Comecra|Comecra]] ([[User talk:Comecra|talk]]) 07:10, 31 May 2012 (UTC)
</blockquote>
:For that I'm not sure. Perhaps a little more research will reveal the answer, but I'll need to do more research. Torr is related to, but not exactly the same as mmHg, just as Kelvin is related to, but not exactly the same as Celsius. Kelvin equals Celsius (Absolute). Hertz is similar to RPM, but also not the same. Hertz is cycles per second, which usually refers to wave forms, whereas RPM is the revolutions per minute of a rotating object. In example, hertz usually refers to the cycle times of an electrical signal, say 60 hertz AC line voltage in the U.S., but 50 hertz in Europe. RPM, on the other hand, is commonly used in engineering, like automotive mechanics, in which it usually refers to the speed at which the crankshaft is rotating. The two cannot usually be used interchangeably without some confusion on the part of the readers. Personally, I think torr is similar. For instance, it's better to knw the absolute pressure when dealing with lighting construction, like making neon signs or flashtubes, because the relative pressure of the atmosphere is inconsequential. Torr is almost always used in the field of lighting. However, when dealing with blood pressure, the absolute system pressure is not nearly as important as the difference between blood pressure and air pressure, which is a better indication of burst pressure. MmHg is almost always used for blood pressure measurements. I'll try to do more research when I have the time, and maybe I'll run across the information about when torr was first used. In the meantime, it's late here, and I need to get myself home. I'll look some more in the morning. [[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 08:24, 31 May 2012 (UTC)

::I only had a few minutes to look this up, and there are some conflicting sources. The ''Oxford English Dictionary'' says torr originated in the 1940s. I find this to be doubtful, because torr is defined in a 1913 version of ''Websters Dictionary'', which says the term first came into popular use "sometime before 1848." The book ''Vacuum Science and Technology: Pioneers of the 20th Century'' says the term torr was being commonly used by the late 1800s and early 1900s by scientists like Edison and Dewar, who, by 1910, were routinely drawing vacuums lower than 10<sup>-5</sup> torr. This sounds more reasonable, as this era is when high vacuum technology was in its infancy. In 1954, torr was redefined to equal 1/760 Atmosphere, which this article already details. [[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 22:24, 31 May 2012 (UTC)

== When was the definition of the torr changed? ==

The article currently says that originally, 1Torr = 1mmHg, but this was changed in 1954 to be 1Torr = 1/760atm. 
However, the reference given to prove this says no such thing! That reference is about a redefinition of the atmosphere (to 101325atm = 1Pa). It doesn't say anything about the torr.
Any takers...?--[[User:Feline1|feline1]] ([[User talk:Feline1|talk]]) 10:55, 18 July 2014 (UTC)

:It is mentioned in the book I discussed one section above this one: ''Vacuum Science and Technologies: Pioneers of the 20th Century.'' Page 92, if I recall correctly. [[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 01:28, 25 July 2014 (UTC)
:::OK and what did that book claim on the matter? :)--[[User:Feline1|feline1]] ([[User talk:Feline1|talk]]) 19:56, 29 July 2014 (UTC)

::::Hmm. Apparently the page is no longer available of google books. I'll check the library the next time I'm there to get an exact quote. As I recall from memory, the first Vacuum Symposium was held that year, where a Committee on Standards was formed for the purposes of coming up with a standardized terminology for use in vacuum measurements. The problem with mmHg is that it is a relative measurement. (For example, a person's blood-pressure may read normal at sea level, but will be very different on Mt. Everest because of the lowered air pressure.) Air pressure is constantly fluctuating, even at sea level. To work in deep-vacuum measurements, they needed an absolute reading which started at zero (zero never fluctuates). Therefore the standard atmosphere was redefined from the zero point to equal 1013250 dyn, and Torr to equal 1/760 atmosphere. (eg: 1 Torr = 1333.224 dyn.) The proceedings of the symposium are detailed in the book ''Advances in Vacuum Science and Technology,'' on page 72. [[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 20:42, 31 July 2014 (UTC)

::::Here we go. I had a little time to do some digging. I can only find the "snippet view" of the afore-mentioned source on google, but see the third listing from the top. It shows most of the pertinent info. https://www.google.com/search?sourceid=navclient&ie=UTF-8&rlz=1T4GGHP_enUS577US577&q=vacuum+edison+dewar+1954#q=torr+definition+vacuum+1954&tbm=bks  [[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 01:29, 1 August 2014 (UTC)

:::::I see. And does that fix the date to 1954?--[[User:Feline1|feline1]] ([[User talk:Feline1|talk]]) 19:26, 2 August 2014 (UTC)

== fraction format ==

For those of us who are used to punctuation every three digits in numbers of 5 digits or more — e.g., 1 AU = 149,600,000 km (US format) = 149.600.000 km (French format?) — the "spaced-out format", 149&nbsp;600&nbsp;000, is a bit unfamiliar but not really confusing, once we get used to it. But when it's squeezed into a numerator in half-height type over a diagonal fraction bar...
: {{frac|{{val|101325}}|760}}
... well, at least some of us are apt to mistake that, if only briefly, for 
: {{frac|101&nbsp;|325|760}}
which of course is entirely different. So I changed it to {{frac|({{val|101325}})|760}}, which is at least unambiguous.

And then I went to [[Template:Frac]] to learn how to wikicode that second example, {{frac|101&nbsp;|325|760}}. And there I read 
: This template should '''not''' be used in science or mathematical articles, per [[MOS:FRAC]] and [[MOS:MATH#Fractions]]; use {{tl|sfrac}} instead.

Oh ho. So: Use
: <code><nowiki>{{sfrac|{{val|101325}}|760}}</nowiki></code>
to get
: {{sfrac|{{val|101325}}|760}}

So I did. But it happened to show on my screen with a linebreak between the number and the unit,
: &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ....{{sfrac|{{val|101325}}|760}} 
: [[Pascal (unit)|pascals]] (~133.3&nbsp;Pa)

So I wrapped it in {{tl|nowrap}}:
: <code><nowiki>{{nowrap|{{sfrac|{{val|101325}}|760}} [[Pascal (unit)|pascals]]}} (~133.3&nbsp;Pa)</nowiki></code>
to get
: {{nowrap|{{sfrac|{{val|101325}}|760}} [[Pascal (unit)|pascals]]}} (~133.3&nbsp;Pa)
which is accurate, conformant to [[MOS:FRAC]] and [[MOS:MATH#Fractions]], and not misreadable.

To discuss this, please {{Tn|Ping}} me. --[[User:Thnidu|Thnidu]] ([[User talk:Thnidu|talk]]) 10:30, 10 March 2015 (UTC)

== google ==

Some parts of this article come up in a Google search, but the fractions don't come through as fractions.  This might take some discussion with actual Google people to fix. [[User:Gah4|Gah4]] ([[User talk:Gah4|talk]]) 21:06, 14 November 2017 (UTC)

== ''manometric units are routinely used'' ==

It seems to me that ''manometric units are routinely used'' when one needs about 2 digits of precision, such that the differences in g and density of Hg don't matter. I was just noticing that natural gas pressures, as input to a furnace, are inches of water. In this case, it would be gauge pressure, as that is what affects a burner. Blood pressure is also about 2 digits. While much of the article makes a big difference comparing torr and mmHg, most often is isn't significant. In the case of high vacuum systems, one digit is about right. [[User:Gah4|Gah4]] ([[User talk:Gah4|talk]]) 21:27, 20 October 2022 (UTC)

:I'm sure that precision has a lot to do with it, if I'm understanding you correctly. By the time Kelvin and Edison we're doing their famous experiments in deep vacuum, they were routinely pulling vacuums that were a full order of magnitude or more deeper than are found in space (10<sup>-5</sup> torr). You need very precise gauges to measure that. In natural gas lines, you don't need high precision. Pressure in the building I'm in right now is measured in PSI, which is between is 2 for low pressure and 5 for high pressure lines. A little more precision is needed at the individual heating units, so each has it's own regulator and are fine tuned in either inches of water or millimeters of mercury (mainly, I suppose as a matter of convenience, because that's also how you measure the various dynamic pressures in the incoming combustion-air). 

:In lighting, high precision is necessary, because it's one of those things where the slightest difference in the beginning can make vast differences in performance down the line. (See: [[Chaos theory]]) One of the biggest problems Edison had, for example, was getting all the oxygen and water vapor out of his lamps. In neon lamps and flashtubes, you can just bombard the glass with high-energy particles and break loose all the water and oxygen, but with other forms of lighting they had to heat it to red-hot temperatures externally and pull very high vacuums to get all the impurities out. That required some very precise gauges to make the process repeatable and reliable. [[User:Zaereth|Zaereth]] ([[User talk:Zaereth|talk]]) 00:13, 21 October 2022 (UTC)
:This is probably right. It might be good to have a source for its ongoing routine use?
:At the moment, the NPL citation given for manometric measurements being discouraged does not have anything to that effect. I also question the use of the generalised passive voice here - discouraged by whom, for what purposes? [[Special:Contributions/51.155.19.253|51.155.19.253]] ([[User talk:51.155.19.253|talk]]) 13:52, 27 April 2023 (UTC)

== Inches of mercury ==

Should the article mention inches of mercury, way too often used in the US? I suspect both absolute and gauge pressure are used, and not always consistently. [[User:Gah4|Gah4]] ([[User talk:Gah4|talk]]) 10:54, 17 May 2024 (UTC)