How come weight difference doesn't cause problems in trade?

[jbriggs444]

Maybe the people who do the weighing know to adjust for it.

See post #8. Or look at this article. http://www.bittermanscales.com/blog/scale-calibration

[attribution repaired]

 

[DrGreg]

DrGreg said: ↑
Maybe the people who do the weighing know to adjust for it.

See post #8. Or look at this article. http://www.bittermanscales.com/blog/scale-calibration

It wasn't me who said that!(Now fixed!)

 

[epenguin]

If you want to do anything practical with the unit, at some point you will need to make a physical object with the same mass as that number of silicon atoms.

Yes, I am saying nothing different from that.

 

[Merlin3189]

...and I didn't realize that the percent error was so large (about 0.5% "lighter" at the Equator than at the North Pole). ...

Yes, I too was surprised by the size of difference. But in the world of commerce I think that is still very small.
In the UK most Wights & Measures legislation is intended to protect individual retail purchasers, who may not have the ability to check their purchases. The principle of caveat emptor is generally assumed to apply to transactions between peer businesses. It would be a matter of contract when there was a disagreement over the quantity supplied.

I don't know if businesses may agree any sort of measure between them, but for retail trade only legally specified "weights" must be used and these are all defined in terms of SI mass, so that there can be no ambiguity, disagreement, nor variation. (Eg. "the pound shall be 0·453 592 37 kilogram exactly." ,“OUNCE TROY = 0.031 103 476 8 kilogram.”;)

As for error the worst case I've found so far is a permissible 9% underweight for small packs sold by nominal average weight and provided that the average weight over a batch is at or above the marked value. This is clearly intended to address the manufacturer's difficulty in accurately controlling and measuring economically, rather than permitting unfair trading. Generally the tolerances are much smaller. For non-packaged goods the general principle is that underweight is not permissible and reasonable overweight is allowed to the extent necessary to avoid the possibility of being underweight. (As far as I can tell, excessive overweight would be an offence!) Using unapproved or seriously inaccurate weighing equipment would be an offence, even if there were no underweight sale.

say you run a company based on the Netherlands or Sweden or some place similar and another company based in some country near the equator orders 10kg of something precious, say gold. You weigh it precisely, but when it is shipped to whomever ordered it, guess what he will tell you: "Look, you a-holes, I ordered precisely 10kg, but received 9.95kg instead, are you trying to scam me?".

Our (UK) Wights & Measures specifically exempts dealings with foreigners! If we sell on goods from other UK (and, at the moment EU) suppliers, we can reasonably rely on their warranty as to packed quantities, but we are expected to check deliveries from foreigners.
If you had contractually specified weight rather than mass, then you obviously ought to have specified a little more carefully where it should be measured. If Free On Board or EXWorks presumably weighing at that point would be implied and you would have specified any variation such as weighing at destination. I really can't see that you have any complaint.

 

[Andreas C]

To be frank, you confused me now...

 

[jim mcnamara]

Hmm. In the US - every state has a certifying agency for scales, gasoline pumps, etc. Every year the scale is re-checked. Which answers most of the confusion.
This handles 'moving the scale' issues. Because it would be new if it were moved from place A to place Q, it then has to be certified for commerce.

This is apparently true in many places in the Western world.

The only issue I know of: livestock scales. A sheepman from Otero Co. NM told me he did not like dealing with the sheep buyers who drove large trucks to his ranch. Disadvantage: they used their own scales instead of his. Meaning that these kinds of scales are off the radar for the standards people. BTW: most ranchers, livestock traders, and stockyards use balance scales and can weigh multiple animals at once. So the 'balance scales are not used' argument is full of exceptions.

Same with junk yards and metal recyclers: Scrap metals are weighed on balance scales, too. Vehicle is weighed coming in, again on exit. Delta is the weight of the scrap.

http://www.nmda.nmsu.edu/scs/licens...ghts-and-measures-licensing-and-registration/

 

[jbriggs444]

The only issue I know of: livestock scales.

If you are not keeping track of whether the animal poops before, during or after getting on the scales, you probably are not keeping track of whether the scale was last calibrated at the North Pole or at the top of Mount Huascaran in Peru.

 

[Andreas C]

Hmm. In the US - every state has a certifying agency for scales, gasoline pumps, etc. Every year the scale is re-checked. Which answers most of the confusion.
This handles 'moving the scale' issues. Because it would be new if it were moved from place A to place Q, it then has to be certified for commerce.

This is apparently true in many places in the Western world.

The only issue I know of: livestock scales. A sheepman from Otero Co. NM told me he did not like dealing with the sheep buyers who drove large trucks to his ranch. Disadvantage: they used their own scales instead of his. Meaning that these kinds of scales are off the radar for the standards people. BTW: most ranchers, livestock traders, and stockyards use balance scales and can weigh multiple animals at once. So the 'balance scales are not used' argument is full of exceptions.

Same with junk yards and metal recyclers: Scrap metals are weighed on balance scales, too. Vehicle is weighed coming in, again on exit. Delta is the weight of the scrap.

http://www.nmda.nmsu.edu/scs/licens...ghts-and-measures-licensing-and-registration/

Balance scales are used for weighing livestock? That's very interesting, how is it done?

 

[jbriggs444]

Balance scales are used for weighing livestock? That's very interesting, how is it done?

Levers. Similar in principle to the scale in many doctor's offices. You move small sliding weights on an arm that moves a lot while the platform moves only a little.

 

[FactChecker]

Levers. Similar in principle to the scale in many doctor's offices. You move small sliding weights on an arm that moves a lot while the platform moves only a little.

If they are like doctor's scales, they will remain correct for any latitude since the weights of all masses will undergo the same percentage change.

 

[jbriggs444]

If they are like doctor's scales, they will remain correct for any latitude since the weights of all masses will undergo the same percentage change.

Not all are. Some I have seen use unequal arm balances with a lever arrangement. A quick Google looking for pictures shows some with what appear to be lever arrangements connecting to a tension scale. Surely many use load cells.

 

[NTW]

Sure, but balance scales are a bit old school, no longer used. When I'm saying "standard weight", I mean the object. Of course it's a standard mass, but for whatever reason, the objects are called weights.

Balance scales are widely used. The well-known 'Toledo'...

If they are like doctor's scales, they will remain correct for any latitude since the weights of all masses will undergo the same percentage change.

Like this one...

But I believe that the OP is right... These somewhat old-fashioned mass-comparing instruments have today been displaced by electronic scales that measure force, and not mass...

 

[sophiecentaur]

If you are a trader of any kind, your 'scales' must agree with local standards. They need to be calibrated to a level of accuracy that's appropriate to the goods you are selling (gold or potatoes).
The Physics doesn't matter.

 

[votingmachine]

For trade purposes, there are few things where the 0.5% is important. And in most cases, you are selling a product in a RANGE, not at a number. If you buy an 8 oz bag of potato chips, you are unlikely to weigh the chips. The package of chips is required to meet the regulations for the label statement (which helpfully explains ... sold by weight, not volume).

In a trade agreement, there is likely to be an agreement on what the quantities are defined as. If you are buying oil, you buy it in "barrels", which are measured with a calibrated pump. If you are buying gasoline, you buy it in "gallons" using a calibrated pump (no matter the temperature, which also has an expansion effect). It is important to take note that if the sale is in MASS, then there is no difference anywhere. If it is in WEIGHT, then it is different wherever the gravity is different.

And scales ARE re-calibrated with standard masses. So if there was a particularly valuable mass-based transaction, then both sides have to use appropriate, science based measurements. Which means using accepted NIST mass standards, and accepted calibration protocols, and accepted measuring devices.

In more cases than not, the manufacturer determines the amount, and affixes a label statement. And a certificate of analysis. And the accountants put the price on it. You often get more than you pay for ... if you order a kilogram of NaCl in a bottle, it is often more than 1000 grams in the bottle.

Gold and precious metals are odd in that they are frequently spoken of in "Troy ounces" (31.1034768 g at 1 g). But they are really being measured in mass. And a 31.1034768 gram mass of gold will have the same mass anywhere.

If you buy gasoline by the tank truck, you get two numbers: the volume of gasoline at ambient temperature, and the volume of gasoline at 15-degrees-C. And you pay for the gasoline at the 15-degreeC temperature, so that you don't pay more on a hot day, and put it underground where it shrinks. When there is money involved, people tend to notice the properties of physical objects, and wrote contracts accordingly.

 

[Khashishi]

This is why we have a National Institute for Standards and Technology (and why it operates as part of the Department of Commerce). It does mostly science stuff nowadays, but was established (as the National Bureau of Standards) to standardize weights and measures.

 

[CWatters]

Temperature can also matter...When a ship stops to refuel they sometimes check the fuel being uploaded isn't too hot.