Author Topic: LOL, US imperial weight standards are base on the Metric System Kilogram!  (Read 21905 times)

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Offline T3sl4co1l

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btw, since it's a derived unit, that also means by definition it's less accurate.

1 inch == 25.4mm, by definition.

Threading lathes with 100/127 conversion gears can cut either thread, exactly. ;)

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Offline theatrus

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The US even tried to metricfy - there are a number of road signs (probably replaced by Caltrans now) listing distances in miles and kilometers. It... didn't go well.
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Online tautech

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We changed back in the 70's just as I was starting work.
The old guys didn't like mm's, reckoned they were too hard to see compared to 1/16 ths.  ::)
Most soon got glasses.  :-DD

Most of the conversions become second nature pretty quick but the one I always had trouble with is the US gallon.
Where on earth did that originate from and what's it related to ?  :scared:
Weight ? Volume ?
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Offline yada

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At 5.00 min in the video he must be wrong stating different displacement volumes in air can cause up to 110mg of difference,
perhaps in water but not in air, somebody got their notes mixed up..  :popcorn:

Yeah that souded way too high. We an figure out airs weight/mass using
Pressure X Vol =nUMBER of mols X R(0.08206) Temp in K.

One kilo of PtIr was 21.5 g/cc / 1000g = vol of little weight thing.

So we take our volume of air at STP X vol of air in mg ad we subtract that from the mass of the weight? Mayb 100mg is right. Air is kind of heavy (I'm assuming air is just 80% N2 and 20% O2.)
 

Offline moz

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At 5.00 min in the video he must be wrong stating different displacement volumes in air can cause up to 110mg of difference,perhaps in water but not in air, somebody got their notes mixed up..  :popcorn:

Air weighs about 1kg per cubic metre at sea level (1 gram per litre), and 1kg @ density of about 20 means the kilogramme has a volume of about 50ml. That much air weighs about 50mg. The stainless steel kilogramme has a density about 1/3rd of the platinum-iridium one, so three times the volume. The extra 2x the volume weighs.... about 100mg. I could find links, but those numbers are either from the video or you should remember them (density of one... come on, how hard is that to remember :))

I think his numbers are right. As you'd hope from a senior NIST representative.
« Last Edit: May 11, 2017, 05:16:46 am by moz »
 

Offline moz

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The best thing about imperial units, sorry, "US convent eunuchs" is that there are so many to choose from. We could look at the displacement question this way: Air pressure is about 15 pounds per square inch. The atmosphere is approximately 480 chains deep but the density drops to nothing at the top so we can say the density at the bottom is probably more like 218 slugs per acre. The specific gravity of platinum-iridium is about 179 pounds per gallon (US gallons) or ... you know, I give up. All those conversions are doing my head in.

But I do love that you measure water in acre-feet, fluid ounces, gallons, pints, cubic yards or quarts. So many choices, none easily relatable to any other. All based on stuff that's readily to hand before the industrial age. So we get really fun units like fluid scruples (which sounds like it should measure corruption but doesn't).
 

Online Dr. Frank

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The inch is also based on the SI standard.
btw, since it's a derived unit, that also means by definition it's less accurate.

Latter is an incorrect statement, but a very interesting one, because this leads to some deep thoughts about ratio determination for any of the SI-units.

At first, 'derived units' are all these, which are derived by powers, products or quotients of the 7 base units.
Examples (relevant for EEVBLOG) are the Ohm (kg·m^2·s^-3·A^-2) and the Volt (kg·m^2·s^-3·A^-1).

The inch is a non-SI unit of length, but it's not a derived unit. Though the inch is not recommended for use, it has the same acceptance, as other non-SI units, but which are still in daily use, like: minute, hour, tonne, litre, etc.

Anyhow, NIST defines conversion factors between the SI definitions and many of the U.S. units.
These factors may be exact or an approximation. https://www.nist.gov/physical-measurement-laboratory/nist-guide-si-appendix-b8

The inch / meter conversion factor is exactly  2.54E-2.
Therefore, the definition of the inch is exact, like the meter.

But there's always the realization (mise en pratique) of units.

The meter is realized via the exact definitions (i.e. zero uncertainty) of the speed of light, and of the second, therefore, any fraction or multiple of the meter can be realized with zero uncertainty - within the experiment precision limits, of course.

So the inch is in terms of definition AND realization as accurate as the meter itself.

The length and the time are defined by invariable constants of nature, therefore universally constant and exact.

Volt and Ohm are currently not exact units, neither in definition, nor in realization (~ 1e-7 uncertainty).
This will also change by SI-2018. Their new definition and realization will turn them into exact units, which are also invariable and universal. The new SI - Volt definition by a Josephson Junction Array also has the big advantage, that any fractions and multiples of a Volt can be realized with zero uncertainty (within experiments accuracy), whereas the Klitzing-Ohm has to be divided by methods, which are not exact.


Now up to the mass / kilogram, that's also different. The current definition by means of an artifact is exact.
Anyhow, this unit is not invariant, as the prototype kilogram and its 40 copies all drift over time, obviously.

The realization of the mass, that means any multiples or fractions of the prototype kilogram, also is not exact, because at first, it's only possible to make a direct comparison to the prototype by balances, which have about µg uncertainty, and the creation of fractions like 500g or 100g is even less precise, because there's no such precise 'ratio machine' for masses. Realization of an ounce is even worse, due to the non-exact conversion factor.

Analogously, before the discovery of the Josephson Junction, ratios of the Volt depended on the Kelvin-Varley-divider (Fluke 720A), or the Hamon-divider (Fluke 752A), ratio uncertainty > 1E-7  only.

The new kilogram definition by means of an exact value for Plancks constant, and the Avogadro constant will allow to make exact copies, and exact fractions and multiples, as comparisons to artefacts are no longer necessary.

You may simply design a Si-sphere to let's say 125g, and determine its exact (currently to ~2E-8 uncertainty) mass by counting its atoms.
In a similar manner, the Watt balance also allows exact creation or measurement of random masses by appropriate variation of its measuring voltage.

This is the 2nd reason and advantage of the new mass definition with SI-2018.

Frank

« Last Edit: May 11, 2017, 10:44:01 am by Dr. Frank »
 
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Offline CJay

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The other fact of the matter is that the US is sort of like the UK when it comes to our use of the Imperial/US Customary systems. In the UK roads are measured in miles, I'd wager to bet they still use Imperial units to measure lumber, bake cakes, and maybe even in some places measure gas.

Nope, we're all metric here apart from our speed limits and road lengths.

Only ten minutes ago I was looking at a sheet of plywood that was 2440x1220mm and 12.7mm thick. Or, as everyone knows it, an 8 by 4 sheet of half inch ply.

We might use metric units but an awful lot of stuff is just Imperial sized.

'Gas' though, I doubt you'd be able to buy anywhere in the UK in gallons, partly because it's not legal to sell in gallons and partly because it's so damn expensive (~£1.20 a litre, roughly $7 an imperial gallon) and it looks cheaper in litres.
 

Online Nusa

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And then there's dimensional lumber, which has changed sizes over the last century while retaining the same names. For instance, a 2x4 now actually measures 1 1/2" x 3 1/2". When I was a kid, they measured 1 5/8 x 3 5/8. Salvaged 2x4's from hundred year old houses are often actually 2" x 4" (and of superior old-growth wood that you can't get anymore).

Lowes lost a lawsuit a few years ago for failing to put actual measurements on their 2x4s. I remember they paid out $1.5 million and updated all their labeling. I suspect some other suppliers did the same to avoid the same fate. Apparently just because it's a industry standard doesn't satisify consumer laws on accurate labeling.
 

Offline CJay

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On a product that changes size depending on how much moisture it has absorbed?

That sounds like a minefield.
 

Offline Ampera

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The other fact of the matter is that the US is sort of like the UK when it comes to our use of the Imperial/US Customary systems. In the UK roads are measured in miles, I'd wager to bet they still use Imperial units to measure lumber, bake cakes, and maybe even in some places measure gas.

Nope, we're all metric here apart from our speed limits and road lengths.

Only ten minutes ago I was looking at a sheet of plywood that was 2440x1220mm and 12.7mm thick. Or, as everyone knows it, an 8 by 4 sheet of half inch ply.

We might use metric units but an awful lot of stuff is just Imperial sized.

'Gas' though, I doubt you'd be able to buy anywhere in the UK in gallons, partly because it's not legal to sell in gallons and partly because it's so damn expensive (~£1.20 a litre, roughly $7 an imperial gallon) and it looks cheaper in litres.

Holy shit. 7$ a gallon? 3$ is expensive where I live. People were dying when it was a little over 4 dollars. It's even worse when you consider that in the UK, a gallon is around .8 of a US gallon.


Most of the conversions become second nature pretty quick but the one I always had trouble with is the US gallon.
Where on earth did that originate from and what's it related to ?  :scared:
Weight ? Volume ?

Isn't it volume? 1 US Gallon = 231 cubic inches.
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Offline CJay

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Holy shit. 7$ a gallon? 3$ is expensive where I live. People were dying when it was a little over 4 dollars. It's even worse when you consider that in the UK, a gallon is around .8 of a US gallon.



Nope, other way round, a US gallon is 0.8 Imperial gallons, ours is 4.55 litres, yours is 3.785 litres so it's not quite as painful. (still bloody expensive though)
 

Offline Ampera

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Holy shit. 7$ a gallon? 3$ is expensive where I live. People were dying when it was a little over 4 dollars. It's even worse when you consider that in the UK, a gallon is around .8 of a US gallon.



Nope, other way round, a US gallon is 0.8 Imperial gallons, ours is 4.55 litres, yours is 3.785 litres so it's not quite as painful. (still bloody expensive though)

rip.

I've been studying for a maths final (Calc 1) and I still can't do maths.
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Offline CJay

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I've been studying for a maths final (Calc 1) and I still can't do maths.

Know the feeling well, the more I learn the less I know
 

Offline iainwhite

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Most of the conversions become second nature pretty quick but the one I always had trouble with is the US gallon.
Where on earth did that originate from and what's it related to ?  :scared:
Weight ? Volume ?

It is based on one of the gallons used in England in the 1700's - the 1706 Queen Anne Wine gallon. (there were others e.g. Ale gallon, Corn gallon)
The UK 20-ounce gallon was not adopted until 1824 (based on the volume of 10 Avoirdupois pounds of water at 62°F) which was after US Independence.
 
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Offline CatalinaWOW

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The other fact of the matter is that the US is sort of like the UK when it comes to our use of the Imperial/US Customary systems. In the UK roads are measured in miles, I'd wager to bet they still use Imperial units to measure lumber, bake cakes, and maybe even in some places measure gas.

Nope, we're all metric here apart from our speed limits and road lengths.

Only ten minutes ago I was looking at a sheet of plywood that was 2440x1220mm and 12.7mm thick. Or, as everyone knows it, an 8 by 4 sheet of half inch ply.

We might use metric units but an awful lot of stuff is just Imperial sized.

'Gas' though, I doubt you'd be able to buy anywhere in the UK in gallons, partly because it's not legal to sell in gallons and partly because it's so damn expensive (~£1.20 a litre, roughly $7 an imperial gallon) and it looks cheaper in litres.

WOW.  That is really mixed up.  You can still buy half inch plywood.  Here in the US we get the plywood in 8 by 4 sheets, but it is usually 12 mm thick, labeled as 15/32.  Looking at the web the plywood industry has generally standardized on metric thicknesses, with length and width most often conforming to the 8 ft by 4 ft size.

So in a metric country you get your plywood in a weird fractional thickness which corresponds to a simple English system fraction, while in a English system country we get our plywood in a weird fractional thickness that corresponds to a simple metric thickness.

Us tree descended apes go to great lengths to make things confusing.
 

Offline Monkeh

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Don't mind CJay, the nominal thickness is a whole number.
 

Offline Galenbo

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Only ten minutes ago I was looking at a sheet of plywood that was 2440x1220mm and 12.7mm thick. Or, as everyone knows it, an 8 by 4 sheet of half inch ply.

We might use metric units but an awful lot of stuff is just Imperial sized.
In our country, only cheap rubbish wood has that size.
Decent quality is always 2500x1250 or 2600x1250.
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Offline Monkeh

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Only ten minutes ago I was looking at a sheet of plywood that was 2440x1220mm and 12.7mm thick. Or, as everyone knows it, an 8 by 4 sheet of half inch ply.

We might use metric units but an awful lot of stuff is just Imperial sized.
In our country, only cheap rubbish wood has that size.
Decent quality is always 2500x1250 or 2600x1250.

In your country you never had an imperial infrastructure.
 

Offline tronde

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In our country, only cheap rubbish wood has that size.
Decent quality is always 2500x1250 or 2600x1250.
I guess the 2500 and 2600 makes a perfect fit to your normal ceiling height in rooms? All countries have traditionally had different heights and therefore different sizes to minimise cutting.
 

Offline RGB255_0_0

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Only ten minutes ago I was looking at a sheet of plywood that was 2440x1220mm and 12.7mm thick. Or, as everyone knows it, an 8 by 4 sheet of half inch ply.

We might use metric units but an awful lot of stuff is just Imperial sized.
In our country, only cheap rubbish wood has that size.
Decent quality is always 2500x1250 or 2600x1250.
These need to be sizes that chippies can work out when their brain is still working in imperial. Youngsters learning from the old guys end up working in inches too when being trained. It's a cycle that repeats ad infinitum so in likelihood will die only when wood working dies. Or whatever other industry.

It's different when it comes to exporting though - there everything has to be standardised one way or another or shit hits the fan.
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Offline SeanB

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I get Chinese made stuff that has fasteners in there that have a metric thread size and pitch, but the head is not a metric size, but a US standard size, so that to assemble the kit i need a 14mm spanner on a M8 bolt, instead of the correct 13mm spanner. Some even have you needing a 14mm spanner for the bolt and a 13mm spanner for the nut, on a M8 standard pitch fastener. Then you get the M10, which can have either a 17, 18 or 19mm head, instead of the required 17mm. Metric socket sets almost invariably do not come with an 18mm socket, though I did get a few Imperial size sockets to compensate there, as they do prove to be quite useful, though there is a difference between 3/8 BSW, 3/8 AF and 10mm AF sockets, but 2 are nearly interchangeable, while the one is definitely not.

Then cursed the manufacturer who decided they would make every fastener a 1/4 BSG thread, forcing me to use up those hard to get 10/24UNF recoil inserts.
 

Offline metrologist

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This too...

 

Online tautech

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Most of the conversions become second nature pretty quick but the one I always had trouble with is the US gallon.
Where on earth did that originate from and what's it related to ?  :scared:
Weight ? Volume ?

It is based on one of the gallons used in England in the 1700's - the 1706 Queen Anne Wine gallon. (there were others e.g. Ale gallon, Corn gallon)
The UK 20-ounce gallon was not adopted until 1824 (based on the volume of 10 Avoirdupois pounds of water at 62°F) which was after US Independence.
:-DD
Thanks, so if this is correct it might seem the earliest Yanks only had empty grog measures on which to do their liquid measurements which has remained unchanged to this day.
How many 100's of years is that ?
Time for change one thinks.
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Offline CatalinaWOW

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Only ten minutes ago I was looking at a sheet of plywood that was 2440x1220mm and 12.7mm thick. Or, as everyone knows it, an 8 by 4 sheet of half inch ply.

We might use metric units but an awful lot of stuff is just Imperial sized.
In our country, only cheap rubbish wood has that size.
Decent quality is always 2500x1250 or 2600x1250.

Do you know why those dimensions instead of say 2000 x 1000 or 2500 x 1500?    The first dimension pair makes sense in that you can line up two sheets on their side with a vertical one, but 2600x1250 will always lead to scrap.
 


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