Talk:Conversion of units/Archive 2004

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? --Doradus 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. --Doradus 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)

The article currently lists just "foot" for the international foot and "foot (American; U.S. Survey)" for the US Survey foot. I think this could confuse a person who was not well-read about US surveying to think that the later version of the foot is used for all purposes in America. I suggest changing the US survey foot entry to foot (U.S. Survey). --Gerry Ashton 19:39, 31 July 2006 (UTC)

In the absence of an objection, I will change the entry as described above. --Gerry Ashton