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To: Richnorth who wrote (75346)	8/21/2001 4:51:55 AM
From: E. Charters	Read Replies (4) \| Respond to of 116762

It would appear to be more consistent with other measurements to use 31.103 It is a confusion and underscores the trouble with all conversions of one weight system to another. Where did they start and what precision did they use? Any table or authority that does not attempt to tell how they converted the base of the system is misleading. To convert systems with comfort, you have to take their respective standards and weigh them to a great precision and assumed accuracy and assume that the worldwide standards are compared to some equal precision. These standards have been changing as the metric or SI (la systeme internationale or french system) is a mass system that adhered to the litre of water at different temperatures at sea level. Where ever that is. Be prepared to excavate the lab to an appropriate level. Remember the bit about pressure too. Waiting for that break in the weather to get standard pressure can be a bore. How is that measured to exactitude? Is it in pascals or bar? Where is the standard bar-pascal stored? Maybe we should measure it all there? Oh! the infinite regression of exactitude! The old imperial system was a weight, not mass, system that equated to some pound stored in london that was supposed to be 7,000 grains. The US always used a different system that was based on some other standard somewhere in Washington that was no doubt different and the Fr. used a platinum brick in Sevres, fr., where that was supposed to equate to a 1000 mils of water (however big they are) measured at STP at sealevel. This has since been changed a smidgen by the way they measure STP and where they measure it. The avoirdupois system and troy use the same grain by agreement so if it were the basis and measured somewhere it is 5760 to the troy pound and 7000 to the avdp pound. The table you referred to should have all its standards so intercompared and it should be consistent. (that would be impossible expensive so we know it is some kind of culled calculation from some assumed starting point. It is unfair as they don't tell us where they start.) Thence their comparison for tons to troy ounces to grams should stand. Let's do this. They say the avoirdupois ounce is 28.349523125 grams. We know from other sources (ok., I cheat) that the Troy ounce is 29,166.66666 to the short ton. So one short ton of 2000 pounds is 32,000 ounces or 32000 X 28.349523125 = 907184.7398 grams. / 29166.6666 = 31.10347680 grams approx. So you are consistent if you take 28.349523 as your converion of ounces to grams. Since 1955 I have seen various conversions of this quantity. 28.37 to 28.34. The less is more often seen. Even if most tables agree they insult our intelligence if they don't tell us how they compared the authoritative standard for the pound (anyone know what that is?) to the authoritative standard for the litre-kilogram. I dare yah to do that. I dare you to be right to 8 decimal places. First of all you have to get one litre of water to the exact temperature which is pretty near freezing. To 8 decimal places. Then of course you have to make sure you have EXACTLY 1000 mils of water at that temp. So your resevoir of water must be at that temp EXACTLY for addition to your scale and bottle. Of course your scale must be a balance accurate to grams to 8 decimal places. Oh dear! Well of course you can balance it to smidgens first and assume grams follow. Quickly grab the world standard for the pound in your frosty room (with appropriate permissions from its keeper and not getting any salt or condensation on it) and slap it on your ultra clean and ultra accurate scale. Measure to 10 millionths of a gram. The problem with gram scale divisions I will leave to you. It's simple. Close to ten millionths of a gram is good enought. I have read of determinations of the litre and gram but they did not do pounds simultaneously so it does not count for conversion. The pound does not have such a standard that compares in precsion-accuracy. I have never seen or heard of it. It cannot be worldwide reproduced to that standard as far as I know. So, there are no exact conversions. It's all a lie for children. Distance conversions are even more ridiculous. No one can measure a foot or mile to any precision. I used to do a lot of surveying and 1 to 100,000 accuracy is as good as it gets. (1/2 inch in a mile). Surveyors struggle with this everday but scientists in lab coats get to do ultra-surveying. We are jealous. As soon as they tell us how the do it we are all switching over. Too bad we didn't have those mile at once ultra measurers on hiways. Sure would have simplified the job, no matter what the capital cost. Again where do you start? At a foot or a mile? Whose foot and whose mile? If you start at the foot, how do you then put 5280 of them together to compare with 1000 metres (and eliminate earth curvature) To do it to the precision of the assumed conversions you would have to do it an evacuated tunnel with three machines and light beam-standards. (The metre is now defined as so many wavelengths of light of a certain frequency). The tunnel comparison hasn't been done. The US mile is now a "defined" metric exact mile. It has been adjusted to come out "even" with the centimetre. It is not an imperial mile. Want to tear pounds of hair out? Try converting US, and imperial fluid measure, gallons, litres, fluid ounces and the like. I guarantee you cannot do it (well or easily). There are no standards of conversion as in pounds. Nobody went into a lab with the respective worldwide standards and did it. It is all guesswork. On top of that imperial fluid ounces and US fluid ounces (.0625 pints) are different weights and volumes. Hairy hairy hairy. Quarts are 40 imperial fluid ounces in Britain. Quarts are 32 US fluid ounces in the US. One gallon US is 8.3453 pounds or 128 US fluid ounces. So a fluid ounce is 1.04316250 avdp ounces. An Imperial gallon is 160 imperial fluid ounces. This is supposed to be ten pounds exactly (of water) as the Imp fluid ounce is equal to the avdp ounce too, (of water), in weight. If gallon conversion is right at 1.20095 US to imp. then the weight of a Canadian gallon, should be 10.0222 pounds. Close. But not. -- 10 grams out is not exact. (Fluid measure conversions by Dorr Oliver Long and Denver Equip. -1967) EC<:-}