Talk:Conversion of units

Contents

1 Don't Suppress Entries 2 Imperial? 3 Alphabetical order 4 Relation to SI units 5 Dunams 6 Natural units 7 Different kinds of feet 8 Article bloat 9 Correct conversion to coulombs? 10 Light Year? 11 Exact/Defined Formatting

Don't Suppress Entries

Before we go off suppressing entries, let's make something clear: this table should be as exhaustive and self-contained as possible. If units are to be removed or moved to a separate table, let's include a link!

Urhixidur 13:53, 2004 Jun 23 (UTC)

Imperial?

I read "Imperial mechanical" and "Imperial electrical" (in Power->horsepower, for example) and have no idea of what does it mean, nor where to look it up. Please insert a link there or make an acclaration somewhere. — Euyyn 12:19, Aug 31, 2004 (UTC)

Patience, we're working on it. The SI units are nearly done, we'll get the Imperial system into shape next. The adjectives serve to put the unit in its system context. Imperial horsepower units are (or were) used in the Commonwealth countries because they were part of the British Empire in the past. Electrical horsepower is used in the electricity industry (to rate turbines, for example), whereas mechanical horsepower is used by engineers with machinery and engines (internal combustion or steam).

Urhixidur 12:49, 2004 Aug 31 (UTC)

Thanks! =) --euyyn 01:07, 12 Sep 2004 (UTC)

Alphabetical order

Should the units be in alphabetical order?

Relation to SI units

The litre is not an SI unit. The SI unit of volume is m³. Yet the column titled 'Relation to SI units' contains litre values. What do people think should be done?

The Litre may not be a "true" SI unit but it is "in use with it" (Système international d'unités (SI) 7ème édition (1998)). It has a simple power-of-ten relation to the cubic metre (unlike the hour and day), so it doesn't obscure the underlying value. I don't think we would gain much in converting all L to dm³, all mL to cm³, all μL to mm³. It wouldn't hurt, on the other hand. To sum up: I don't really object, but I won't do it myself.  :-)

Urhixidur 12:58, 2004 Oct 24 (UTC)

Dunams

Someone should include the Dunam in the Area section. Just to be really complete.:-) I would, but my concept of math and such is poor. --Penta 02:36, 27 Oct 2004 (UTC)

Natural units

Maybe we should add in conversions to natural units, or even a column. Because natural units are indeed the only truly cosmological constant units we have. That sounds important enought to warrant an entry, or even to warrant a column (since they're much more cosmological that say SI units). GWC Autumn 57 2004 13.30 EST

Different kinds of feet

Is it really true that there are five definitions of the "foot" (the normal one, Sear's, Indian, Benoît, and U.S. Survey) that differ among themselves by only +/- 0.6 microns? Do we have references for all these? --P3d0 16:01, Dec 24, 2004 (UTC)

Foot (British 1865) J. S. Clark's value of 0,304800837 metres (A. G. Bomford, "The Re-adjustment of the Indian Triangulation", Survey of India Professional Paper 28; 1939)

Foot (U.S. Survey; American) (Kasson) Metric Act of 1866 (Public Law 39-183) defines 1 m = 39,37 in exactly

Foot (Benoît) Jean-René Benoît (1841?-1915?) gives the 1895 British yard-metre ratio as 39,370113 inches per metre (or 0,9143992 metres per yard). Used in West Malaysian mapping. Refs: A. Guy Bomford (1899-1996), "Geodesy", 2nd edition 1962; after J. S. Clark, "Remeasurement of the Old 10-ft. Length Standards of the Ordnance Survey"; Empire Survey Review no. 90; 1953) Michelson, Albert Abraham & Benoît, Jean-René, 1895, Détermination expérimentale de la valeur du mètre en longueurs d’ondes lumineuses, Bureau international des poids et mesures, Travails et Mémoires 11, 1.

Foot (Indian) 0,99999566 British feet (A. R. Clarke 1865). British foot taken to be J. S. Clark's value of 0,304800837 metres (A. G. Bomford, "The Re-adjustment of the Indian Triangulation", Survey of India Professional Paper 28; 1939)

Foot (Sears) Sear's 1922-1926 British yard-metre ratio as given by Bomford as 39,370147 inches per metre (A. G. Bomford, "Geodesy", 2nd edition 1962; after J. S. Clark, "Remeasurement of the Old 10-ft. Length Standards of the Ordnance Survey"; Empire Survey Review no. 90; 1953); also given as 1 ft = 0,30479947 m (Australian Land Information Group http://www.ga.gov.au/nmd/geodesy/datums/history.jsp)

Foot (Clarke's; Cape; South African Geodetic) Alexander Ross Clarke's (1828-1914) 1858-1865 ratio of 1 British foot = 0,3047972654 French legal metres. Used in older Australian, Southern African & British West Indian mapping. (Australian Land Information Group http://www.ga.gov.au/nmd/geodesy/datums/history.jsp; see also J. S. Clark, "Remeasurement of the Old 10-ft. Length Standards of the Ordnance Survey"; Empire Survey Review no. 90; 1953)

Urhixidur 18:17, 2004 Dec 24 (UTC)

Uh... Wow. --P3d0 20:37, Dec 24, 2004 (UTC)

The only feet still in use nowadays are the "international foot" (the usual foot of 12 times 2.54 cm) and the U.S. Survey Foot. The others are historical curiosities now.

Urhixidur 05:42, 2004 Dec 25 (UTC)

No, the U.S. Ac of July 28, 1866 did not redefine the foot. The U.S. Treasury department had, back in 1832, defined the standard yard as

"the 36 inches between the 27th and 63d inches on a certain brass bar, commmonly designated as an 82-inch bar, prepared for the Coast Survey by Troughton of London. Hassler had brought this bar to the United States in 1815, after he had been detained in Europe for several years by the War of 1812. The 36-inch space referred to was supposed to be identical with the English standard at 62 °F, although it had never been directly compared with that standard.

"It is evident from Hassler's reports that he regarded the English yard as the real standard of length of the United States and the Troughton scale merely as a copy whose length should be corrected if it ws subsequently found to differ from the English yard; and this view was taken by others who subsequently had charge of the standards, as will be shown later on."

U.S. National Bureau of Standards, Weights and Measures Standards of the United States: a brief history, NBS Special Publication 447, orig. iss. Oct 1963, updated Mar 1976, p. 6

That remained the situation in the United States until the Mendenhall Order of 5 Apr 1893 redefined the yard as 3600/3937 meter. Ibid., pp. 16-17

The Act of July 28, 1866 only provided approximate conversion factors. It did not claim to redefine the foot or any other unit. (As far as intent of Congress goes, I would think that a certain number of Congressmen probably thought that this law "defined" the metric units, and that none of them thought it "defined" the customary units.) But the main thing is that this statute was not internally consistent enough to serve as definitions. Why would you pick the conversion factor 1 m = 39.37 as a definition, rather than the other conversion factors given there? It also said a myriameter equals 6.2137 miles (corresponding to a meter of 39.3700032 in), and that a millimeter equals 0.0394 in (1 m = 39.4 in). It did not mention yards in the length section (yards are the units primarily defined in both the Mendenhall order of 1893 and the Federal Register Notice of July 1, 1959 giving the current definition). In addition, the given conversion factors for gallons, bushels, cubin inches, fluid drams, and acres, square yards, and square inches, would result in several other slightly varying definitions of the foot, if these were indeed intended to be definitions. Gene Nygaard 05:35, 27 Dec 2004 (UTC)

I erred in citing the 1866 law for the U.S. Survey foot; according to NIST Special Publication 811, it is the 1893 definition that is used.

Urhixidur 00:18, 2005 Jan 3 (UTC)

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Article bloat

I think it is time to discuss and try to reach some consensus on the scope of this article. I'll throw out some of my suggestions to get the ball rolling. For example, when editing it we get a message about trying to restrict it to 32 kilobytes, and we could easily do so.

If nobody cares enough to discuss it, I'll just start editing in accordance with these principles.

• This article should only list units which have seen some significant use in the 20th century or later, at least in some geographical location or field of activity. Leave the rest to medieval weights and measures or ancient weights and measures.
  • In his 1790 report to the House of Representatives, Thomas Jefferson made this characterization:[1] (http://ourworld.compuserve.com/homepages/Gene_Nygaard/t_jeff.htm) "coomb, dry; this last term being ancient and little used." This unit has seen no revival since then.

• There is no need to list every variant definition in use.
  • Yes or no?
    • The difference between imperial gallons and U.S. liquid gallons, yes.
    • The difference between the international foot and the 1893-1959 U.S. foot still used in USGS surveys, debatable.
    • The difference between the Paris pied (foot) and the Quebec pied, definitely not. In this case, neither unit has been used before the 20th century, so I'd say they don't belong here at all.
  • Include one or two identified variants of the Btu and the calorie; leave the rarely used ones to the respecive articles on the units.

• There is no need to list every historical variation in the definitions. Leave that to the specific article on that unit.
  • The distinction made here between torrs and millimetres of mercury is silly. Both names are used now with the definition listed under torr; both names were used in the past with the older definition listed under millimetre of mercury. Combine both names under the current definition.

• When compound units include a component of time, volume, or area, there is no need to list every possible combination of hours, minutes, seconds, years, etc.; nor every Cubic centimetre, millilitre, cubic millimetre, decilitre, cubic metre, etc. Pick the ones in common use; forget the others.

Gene Nygaard 19:16, 2 Jan 2005 (UTC)

I agree that a lot of conversion factors could/should be pushed out to the relevant articles (e.g. the various feet). Key variants such as the U.S. vs Imperial values ought to be kept, that is obvious. So should the U.S. Survey units —at the very least the mile ("statute mile"). The distinction between torr and mmHg may seem silly to some, but is nevertheless real.

The problem with paring the list down, farming sublists out to articles, and so on, is that one then no longer has the convenient master list in one place. If we're worried mostly about the list's size, the first step should be to make each section into a separate page (e.g. "Conversion of units (Volume)" and so on). Similarly, removing some divisions (per minute, per hour, per day, etc.) for convenience's sake is no good —one user's most frequently used magnitude won't match another, depending on context. Flow rates in oceanography won't be in the same ranges as flow rates for home air infiltration measurements, for example. In that sense, "common use" is not definable.

Urhixidur 00:13, 2005 Jan 3 (UTC)

There are not two different units called "torr" and "millimeter of mercury". There is an older definition for this unit under either name based on a conventional density of mercury at 0 °C, and there is the current definition of this unit under either name as 1/760 of a standard atmosphere defined as 101.325 kPa. Torr and mmHg only have one joint Wikipedia article, and quite properly so. Historical variations can be dealt with on that page, just like no-longer-used definitions of feet.

Most of what I'm talking about should not be "farmed out"; some could be made clearer in the individual articles linked to here.

I have no problem with flow rates or various other combinations of units actually used to some significant extent. Many of them listed here are not.

This article is linked to from other articles to provide guidance in making conversions from units that might be encountered in that context, and as a reference source for those Wikipedia editors trying to add conversions to measurements already existing in other articles.

It doesn't need to be cluttered up with useless things such as inches and leagues based on the U.S. survey foot, which are never used.

It doesn't need every historical variation in different units.

Things which are not units of measurement

• It doesn't need trivia like various multiples of wine bottle sizes, never used as "units of measurement" as such but only as particular standard sizes, and furthermore which varied in size depending on the size of the prevailing "standard bottle" (now 750 mL, not the size used here).
• Other things never actually used as "units of measure" include "link (Ramden's, Engineer's)" where link can be used to refer to a physical part of the measuring device, but the results of the measurement are expressed in "feet"—units already listed here and readily available for conversion. Whenever "link" and "chain" are used as units of measurement, it is a virtual certainty that it is "Gunter's chain" that is referred to. There is absolutely no ambiguity to worry about.

Gene Nygaard 16:38, 26 Jan 2005 (UTC)

Correct conversion to coulombs?

What is the correct conversion factor from faradays to coulombs? Faraday says 96485.3415, but conversion of units says 96485.3383. Is either one of these an "accepted" conversion value? (message posted to Talk:Faraday and Talk:Conversion of units.) --bdesham 13:58, 8 Apr 2005 (UTC)

I would guess that it depends on the actual definition of those Fred Flintstone units (faradays) which is being used, something that is time-dependent and field-of-activity-dependent. Do you remember the days when faradays were still used, and when physicists defined atomic weight differently from the way chemists defined it, when both were different from the current unified atomic mass unit? Gene Nygaard 14:05, 8 Apr 2005 (UTC)

No, I'm far too young for that :-) In any event, though, the article(s) should be changed to reflect the potential differences in the definition of the faraday—I'd do it myself, but obviously, I don't know enough to do that. --bdesham 18:56, 8 Apr 2005 (UTC)

Light Year?

Is there an official definition of a light-year anywhere? Whoever supplied the figure listed here apparantly used a Julian year. Is it really officially defined as such, or is it not a formally-defined unit?

Exact/Defined Formatting

I think splitting the "Relation to SI Units" columns into "Definition" and "SI Equivilency" or something to that effect would make the mess of numbers much clearer. I can do this if there is no objection. Prometheus235 18:58, 16 Jun 2005 (UTC)

Kudos to User:Crissov for doing the def. column. I tried to polish up the length table to make it more intuitive between exact, defined, and approx. quantites, here's the first bit of it:

Key:

• () Repeated digits, e.g. 1/11 = 0.09(09)
• Bold Exact quantities

Length, l

Name of unit	Symbol	Definition	SI equivalent
metre (SI base unit)	m	co × (1/299 792 458) s	1 m
inch	in, "		2.54×10-2 m
fermi, femtometre	fm	10-15 m	10-15 m
x unit; siegbahn	xu		1.0021×10-13 m
stigma, picometre	pm	10-12 m	10-12 m
Bohr radius; atomic unit of length	a0, b; au	α/(4πR∞)	5.291 772 083×10-11 ± 19×10-20 m
ångström	Å	10-10 m	10-10 m
micrometre, micron	µ, µm	10-6 m	10-6 m
twip	twp	1/1440 in	1.763 (8)×10-5 m
mil; thou	mil	10-3 in	2.54×10-5 m
mickey		1/200 in	1.27×10-4 m
point (ATA)	pt	0.013837 in	3.514 598×10-4 m
point (PostScript)	pt	1/72 in	3.52(7)×10-4 m
point (metric)	pt	3/8 mm	3.75×10-4 m
point (Didot; European)	pt	1/72 French royal inch	3.759 715×10-4 m

I more or less removed superfluous digits, converted it all to meters w/ sci. notation, filled in definitions, etc. I'd like some feedback before I go and do everything. -- Prometheus235 21:04, 20 Jun 2005 (UTC)

I prefer engineer style, x·10^3·n, but scientific style should be fine. I also prefer · over ×, but × seems to be more common in English usage. Equals sign etc. have an advantage when copying to plain text. Christoph Päper 21:54, 20 Jun 2005 (UTC)

I'd actually prefer the ˙ and eng notation (for some quantities), but × seems to be more prevelant in WP. I'm trying to move away from all the equals, approx, equivalent to signs because they are generally confusing, as far as copying into plaintext it doesn't seems that important, most users would probably only be interested in one of the quantities so wouldn't mind a missing sign. I'd also like to sort the units differently, so users wouldn't have to sift through the dozens of obscure units to find a more common one, however I'm not exactly sure how. -- Prometheus235 23:20, 20 Jun 2005 (UTC)