I cracked the mystery of Chinese precision jewelry scales

[magic]

There is a lot of cheap digital scales out there, typically small and battery powered. Basic ones have 3~4 digits, 0.1g or 0.01g resolution at best and cost peanuts, but for some $40 it's possible to get scales with advertised 1mg resolution and 50~200g capacity, such as this "One Hung Low 8068-series Professional Digital Jewelry Scale" piece of sh!t I had a pleasure of testing today.



Amazingly, this scale collects a lot of positive reviews on auction sites, including people saying they tested it with calibration weights and/or compared against professional lab scales.
Well, I can only hope that they got paid for those reviews because if they did it for free they have to be irredeemable idiots

It's not hard to notice that something is off. The scale ships with a calibration weight included and sure enough, calibrating the scale and weighting the calibration weight gives 100.000g as expected, as many times as you want. But then you take it off, put some random junk and suddenly re-weighting the junk gives results that vary by 2~4mg That's if you are lucky and it's a light junk, because heavy junk (like 160g) may vary by 13mg.

Actually, 0.08% is not a terrible result, but how is the 100g cal weight always coming bang on? I guessed the answer quite fast, and that's what really pissed me off. Yes, they cheat and the results are rounded to nearest full grams. More detailed testing near 1g revealed that results which the scale believes to be ±10mg away are shown as 1.000g, some results further still are displayed as 0998~1.002g, near 1.030g it flips randomly between honest reading and 1.003g and further it works normally. Similar behavior was observed near 2g and 3g and that's where I stopped caring about this turd anymore.

Below is a linearity test I conducted by weighting increasing number of identical metal washers, 50 pieces ~33mg each. Blue is the reading, red is deviation from linear fit multiplied by 100. The washers are not calibration weights, they may not be identical and this may contribute to some of the vertical "noise". We see that measurement-to-measurement noise is 5mg peak-peak (including contribution by washers). There is some waviness at the beginning, which could be nonlinearity or - perhaps more likely - drift. (Drift could be cancelled by re-taring the scale between each measurement, which I didn't do.) And then there is a 20mg "glitch" near 1000mg, because the scale assumed that I am testing it with a 1.000g calibration weight and didn't believe its own sensor, which in itself actually seems far more accurate than 20mg

Can't wait for DMM manufacturers to catch the idea, if they haven't already
(Yes, I know that Zotek hides offset voltage of their meters by replacing low readings with zero, I want more )

[Whales]

Hmm.  I've noticed some of my kitchen electronic scales suspiciously landing on exact .00 numbers quite a few times.  I wonder if it's a common chipset feature -- worth checking scale balance datasheets.

[Ed.Kloonk]

 

[magic]

I forgot to mention that the cheating is somewhat stateful. Sometimes when I weighted 1.005~1.015g in multiple pieces, the scale showed 1.000g and then as I removed the weights, it reported the differences correctly and subtracted them from the reading until it went negative and remained below zero with an empty platform

I also noticed that the reading tends to change by 3 counts more often than by any other number. It occurred to me that 3 is what happens when 200000mg is divided by 65536 counts of a 16 bit ADC. I'm still not sure where the other variation comes from, maybe it's oversampling/interpolation or some drift compensation, or maybe I'm wrong about 16 bits.

I would love to see what's inside, but I'm not sure how to dismantle it safely and I don't feel like dumping $40 down the drain - it's going back to the seller.

[magic]

Hmm.  I've noticed some of my kitchen electronic scales suspiciously landing on exact .00 numbers quite a few times.  I wonder if it's a common chipset feature -- worth checking scale balance datasheets.

There is probably some firmware there. I doubt that any documentation could be found publicly and in English but you can try.

[SeanB]

AS I actually have a set of reference mass pieces, I have done the check and verify step on a number of those small units. Those with a calibration mass will read exactly, because they have been calibrated with that mass, using a 2 point calibration, so setting the zero point, and full scale. Not going to say much for the linearity, as the better units will have at least a 3 point calibration step, with a zero, half scale and full scale calibration point, allowing the internal microcontroller to do a best fit curve, for the conversion from ADC counts to display reading.

Have seen pretty good linearity, at least to within 1%, on them, with just that 2 point calibration, though best is to not rely on that, and instead use a check mass at close to your desired mass.

The same basic load cell, the same signal conditioning blob is used for a lot of them, with full range ranging from 40g to 1kg, but the exact same unit, just the calibration is different between them. Sadly no real way to calibrate them, you can only do the same as the original manufacturer, but you can at least use a certified mass piece to do it, instead of the cheap close to mass one they give.

Bought a set of those from China, and took them, figured out how they adjusted it (undo the top cap and drill down to lower, and add lead to raise) so I could get them to agree closer to the recently calibrated mass meter, accurate to 0.5mg. Then sent them in to be certified. Cost more than the masspieces cost originally, but well worth it, as I then knew, down to the milligram, the exact mass, and traceable via 3 hops to the standard kilogram.

[HighVoltage]

What great idea!
To make it more real, they should have the least significant digit change a "little"

To be accurate in 1 mg is not that easy.
I have repaired lots of mg scales and it is amazing what effort the real manufacturer put in scales to make them reliable.
My most precision scale goes down to 10 ug and it is mind twisting what is needed to make that happen.

What surprises me is that so many fall for these cheap Chinese scales.

[gamalot]

Multimeter manufacturers have done something similar a long time ago, the famous Agilent/Keysight multimeters will show zero at very low AC currents. I also know of some scale manufacturers that track zero drift and "cancel" it. Of course, none of them are as smart as this jewelry scale maker! 

[Gyro]

What great idea!
To make it more real, they should have the least significant digit change a "little"

To be accurate in 1 mg is not that easy.
I have repaired lots of mg scales and it is amazing what effort the real manufacturer put in scales to make them reliable.
My most precision scale goes down to 10 ug and it is mind twisting what is needed to make that happen.

What surprises me is that so many fall for these cheap Chinese scales.

My 1ug resolution [Edit: non-Chinese] scales. 

[HighVoltage]

My 1ug resolution [Edit: non-Chinese] scales. 

WOW!
How old is that one ?
And who is the manufacturer?
That must be a very special 1ug scale !

My 10ug scale is about 10 years old from Mettler Toledo, Made in Switzerland.

[free_electron]

just say no and buy a  sartorius or mettler scale

[Gyro]

My 1ug resolution [Edit: non-Chinese] scales. 

WOW!
How old is that one ?
And who is the manufacturer?
That must be a very special 1ug scale !

My 10ug scale is about 10 years old from Mettler Toledo, Made in Switzerland.

It's a Stanton Instruments MC1A  http://stanton-instruments.co.uk/page19.html

It pre-dates the 1960 catalogue, but irrc, it's 1950s (there's a datasheet in the Catalogues section of the above web page). I still have the original calibration/periodic inspection card somewhere, it originated from the Atomic Energy Research Authority Establishment at Harwell, but I picked it up in a 'treasures' shop around 40 years ago. I don't like to think what it was used to weigh, but I went over it very thoroughly with a Geiger counter.

I should probably clarify that the page says that the early models were only good to 2-3ug resolution in practice, probably also depending on the remaining sharpness of the Agate knife edges and synthetic Sapphire planes.


P.S. That site is an interesting resource, I only found it today!

[AVGresponding]

What great idea!
To make it more real, they should have the least significant digit change a "little"

To be accurate in 1 mg is not that easy.
I have repaired lots of mg scales and it is amazing what effort the real manufacturer put in scales to make them reliable.
My most precision scale goes down to 10 ug and it is mind twisting what is needed to make that happen.

What surprises me is that so many fall for these cheap Chinese scales.

Oooh, do you have any repair threads relating to these? I have a very poorly A&D GX-600, it would be useful to read something like that!

[Bud]

There you go, a look inside a no-shit precision scale 

https://youtu.be/eKsEmukmByI

Edit: The video even includes the mandatory Lab cat, though with a twist 

[magic]

Those with a calibration mass will read exactly, because they have been calibrated with that mass, using a 2 point calibration, so setting the zero point, and full scale.

Doubly so if they also round 99.990g to 100.000g

Not going to say much for the linearity, as the better units will have at least a 3 point calibration step, with a zero, half scale and full scale calibration point, allowing the internal microcontroller to do a best fit curve, for the conversion from ADC counts to display reading.

I have seen them too and wondered if it's because they are better or because they are worse and need it more. Maybe I should construct some ~50g test weights and check the midpoint INL of mine, since I haven't returned it yet.

That being said, it's not very important to me. I'm currently looking for good linearity below 10g, for ratiometric measurements on low quantities. I picked the 200g version figuring it may come in handy in the future.

Similar behavior was observed near 2g and 3g and that's where I stopped caring about this turd anymore.

Never say never

New linearity measurement.
The extra 1980mg is a container which enabled easy taring between measurements.
Each measurement was repeated 3 times and the median was used.
Noise is similar but drift is gone, only some unexplained issue at 2~5 and 11.
Good linearity except near 2000mg and 3000mg, as expected

[Zucca]

Bastards! They will burn in hell for eternity.

[SiliconWizard]

Oh well. Cheating for calibration or testing purposes... who does that...
Remember VW?

[Circlotron]

I've got an old Sabtronics frequency counter that does something similar. After running both it and the new-at-the-time Rigol DG1022Z function generator (1 ppm accuracy) for 24 hours I put 10 megs into the counter. It displayed 10000000.0 Hz. Dang! That's good I thought. Wasn't drifting either. Then I dropped it to 9 megs and it showed maybe 7 or 8 Hz low. Similar with 8 megs. Basically the error was  a fixed proportion of the measured frequency, as you might expect. But not at 10 megs...

Dieselgate.
Partygate.
Countergate.

https://www.radioexperimenter.us/rm-1981-05/to-shield-1.html

Edit -> Oh yeah. SiliconWizard beat me to it.

[Bud]

Drug dealers are not going to be happy reading this thread 

[HighVoltage]

What great idea!
To make it more real, they should have the least significant digit change a "little"

To be accurate in 1 mg is not that easy.
I have repaired lots of mg scales and it is amazing what effort the real manufacturer put in scales to make them reliable.
My most precision scale goes down to 10 ug and it is mind twisting what is needed to make that happen.

What surprises me is that so many fall for these cheap Chinese scales.

Oooh, do you have any repair threads relating to these? I have a very poorly A&D GX-600, it would be useful to read something like that!

Sorry to say, that I did not post any scale repair threads
I probably will repair more in the future and then post it on eevblog

[Bicurico]

When I started to read OP, I immediatly thought that the included sample/caliber had a magnet inside...

perhaps I should sell that idea to chinese manufacturer.

[SilverSolder]

Wow, that's lame!!   

I guess you could get around this problem by adding a small, accurate mass to the scale if measuring near a round number....

[AVGresponding]

When I started to read OP, I immediatly thought that the included sample/caliber had a magnet inside...

perhaps I should sell that idea to chinese manufacturer.

  Me too!

Though for extra calibration accuracy, the manufacturer could make several different reference weights, each with a different rfid tag in...   

[SiliconWizard]

Drug dealers are not going to be happy reading this thread 

Maybe the "hobbyist" ones. 

The "serious" ones probably make way enough money to buy decent scales, not cheap crap off Aliexpress.

[magic]

This damn scale is either very good at cheating or it is actually very good except for the cheating

I wanted to do the 0-100g INL test. I found four AA cells which weight about 24g each, numbered them 0,2,4,9 for certain reason and weighed all four of them and then divided them in different sets of 1, 2 or 3 cells and weighed the sets alternately.

This was to hopefully confuse the scale should it try to remember previous results and assume that it is being tested for linearity and lie
Yes, I'm paranoid. Not sure if sufficiently?

The results are below. Each measurement was repeated five times allowing the scale to go back to zero in between. Lines starting with -> are median results. Repeatability was fairly good today and I found that linearity error is virtually nonexistent. One of the 50+50=100 comparisons is spot on, the other is off by 2mg. The 25+25+25+25=100 is off by 5mg, or we could say that each cell was undermeasured by 1.25mg because 100g is supposed to be calibrated. It could easily be quantization error. The 25+25=50 and 25+25+25=75 sums are off by similar margins. All errors are less than 0.01%.
 

Code: [Select]

0249
95.448
95.448
95.451
95.450
95.451
-> 95.450

09/24
47.787
47.662
47.790
47.661
47.787
47.662
47.788
47.661
47.790
47.662
-> 47.788 / 47.662

024/9
71.564
23.886
71.561
23.887
71.563
23.886
71.563
23.890
71.562
23.886
-> 71.563 / 23.887

049/2
71.629
23.820
71.630
23.818
71.631
23.816
71.630
23.819
71.630
23.818
-> 72.630 / 23.818

0/4
23.897
23.843
23.899
23.841
23.898
23.842
23.899
23.841
23.896
23.843
-> 23.898 / 23.842

04/29
47.739
47.707
47.741
47.707
47.742
47.708
47.741
47.707
47.742
47.710
-> 47.741 / 47.707

[magic]

This scale has a drug dealer's mode

How to enter:
- prepare a 15.432g reference weight
- enter cal and place the weight instead of 100g
- switch display units to grains
- multiply readings by 10 to get grams
- (yes, it would be easier to cal with 10g instead, but my scale doesn't accept that)

Right off the bat, noise and short term repeatability are down to ~1mg with a bit of mental lowpass
It's looking like the ADC might be the bottleneck in normal operation
Drug dealing mode probably kicks some frontend PGA into higher gain and overcomes it.

I will test it tomorrow. And how cheating works in grains, because I have no idea.
 

[magic]

Nevermind, this POS is utterly hopeless and unfixable.

In any unit other than grams it still lies, and...
wait for it...
it still rounds to full grams

I have seen youtube reviews of similar scales by guys using them to measure bullets and powder charges (in grains).
Well, hate to be the bearer of bad news, but...

[Kleinstein]

There is even a chance to find some kind of cheating with more expensive scales: It sometime comes with +0 and -0 reading. So the bin for showing 0 gets about twice as wide. I don't remeber the brand were I have found this, but it was a lab balance from one of the big players.

The + and- zero reading can also effect some cheap DMMs (with dual slope ADC) - in this case not a SW problem, but a HW weakness.
Such things may also happen by accident, when rounding and converting to decimal.

[HighVoltage]

There was a time that I liked KERN scales from Germany a lot.
One day I bought a broken KERN lab scale on ebay and thought I could at least try the repair.

That scale was so badly built that by opening the scale, the stiff cables got ripped out of display PCB.
Everything was built for a one time assembly and not to be repaired.
This scale most likely was built in China but hat the "Made in Germany" label on it.
Since that time I stayed away from KERN scales.

So, not only Chinese scales are bad!

This is also true for calibration weights!
I bought a 1kg calibration weight on ebay a few years ago and it has a M4 set-screw in the bottom. So, naturally I took it out and wondered why there was a screw. Well, I found sand grains behind the screw to adjust the mass of the weight. And this weight was of the F1 class!
Unreal!
 

[PlainName]

sand grains behind the screw to adjust the mass of the weight

Is that particularly bad? I mean, so long as it doesn't drift and actually weighs what it's meant to, seems a cheap and quick way to get it done. Also, if you drop and chip it, it's not the end of the world.

[gamalot]

sand grains behind the screw to adjust the mass of the weight

Is that particularly bad? I mean, so long as it doesn't drift and actually weighs what it's meant to, seems a cheap and quick way to get it done. Also, if you drop and chip it, it's not the end of the world.

It gets heavier when it absorbs moisture and vice versa.

[PlainName]

ok

[CatalinaWOW]

I'm more with Dunkemhigh on this.  Much sand is largely silicon dioxide which is going to absorb very little moisture.   A grain of sand is on the order of 10-15 mg.  So the few grains of sand would have a mass of something like 50 mg.  The tolerance on an F1 1kg mass is 5 mg, so the sand would have to change its mass on the order of five percent to put it out of tolerance.  And that assumes the set screw didn't seal the cavity.  Of coarse it is possible that this sand is beach sand which in some cases has a high proportion of calcium carbonate.  Bigger problem then, but the point is that this weight may be an honest weight.  The presence of this trimming technique doesn't seem to me to prove that it is junk.  It seems to me the much larger volume and surface area of brass would be a larger problem than the few grains of sand in this weight.

I would be worried about a sand filled weight where the sand provided a large fraction of the total mass.  Surface absorbtion on the very large resulting surface area would be a likely problem and even modest amounts of bulk saturation would matter.
 

[gamalot]

I'm more with Dunkemhigh on this.  Much sand is largely silicon dioxide which is going to absorb very little moisture.   A grain of sand is on the order of 10-15 mg.  So the few grains of sand would have a mass of something like 50 mg.  The tolerance on an F1 1kg mass is 5 mg, so the sand would have to change its mass on the order of five percent to put it out of tolerance.  And that assumes the set screw didn't seal the cavity.  Of coarse it is possible that this sand is beach sand which in some cases has a high proportion of calcium carbonate.  Bigger problem then, but the point is that this weight may be an honest weight.  The presence of this trimming technique doesn't seem to me to prove that it is junk.  It seems to me the much larger volume and surface area of brass would be a larger problem than the few grains of sand in this weight.

I would be worried about a sand filled weight where the sand provided a large fraction of the total mass.  Surface absorbtion on the very large resulting surface area would be a likely problem and even modest amounts of bulk saturation would matter.

Even though sand doesn't really make a big enough change in weight, filling the weights with sand makes consumers feel cheated. I don't know how much HighVoltage spent on eBay for his weights, a 1kg F1 grade weight in China costs about $40 and doesn't have any screws on the bottom.

[HighVoltage]

Even though sand doesn't really make a big enough change in weight, filling the weights with sand makes consumers feel cheated. I don't know how much HighVoltage spent on eBay for his weights, a 1kg F1 grade weight in China costs about $40 and doesn't have any screws on the bottom.

The screw was not even tight or even real good fitting.
It was one of those threads that was far too loose to call it a fitting threaded screw.
In other words, shaking the weight a lot would probably loose the screw over time.
I don't know, to me that looked like a really cheap way to make a calibration weight.
The opportunity to make a picture was missed!

I have now a really good quality F1 class weight, that came with a note to not touch with bare hands.
Actually a real good calibration weight has a soft cloth within the box to protect the weight.

[Gyro]

This is also true for calibration weights!
I bought a 1kg calibration weight on ebay a few years ago and it has a M4 set-screw in the bottom. So, naturally I took it out and wondered why there was a screw. Well, I found sand grains behind the screw to adjust the mass of the weight. And this weight was of the F1 class!
Unreal!

At least it's a metric screw! 

[HighVoltage]

Here are some examples of really good calibration weights with certificate.

No screw, no sand and no fingerprints.
Both came with a nice cloth for handling.

[jfiresto]

Here are some examples of really good calibration weights with certificate.

No screw, no sand and no fingerprints.
Both came with a nice cloth for handling....

Have you taken your weights to the local Eichamt to check their accuracy? Ours is very friendly but can only compare to no better than F1-class weights.

[HighVoltage]

The "Eichamt" here is not so friendly, they are a profit center and like too much money.

But a local scale repair service tested them for me.
The Sartorius 2kg F2 weight was measured to be:
2 kg + 1,6 mg with an uncertainty of 2,0 mg

So, its mass is 2.000,0016 Gram

[Slartibartfast]

What surprises me is that so many fall for these cheap Chinese scales.

What do you mean by that? Who "falls" for those scales? I guess you cannot mean all those who buy them? It is as with other tools: You need to take into account their limits.

I have one. I use it mostly to balance the relative amounts of binder and hardener when mixing epoxy. I do not need a scale with 50000 counts (or whatever it is that mine has), and in particular for that application I do not need any accuracy, just a little resolution! And the resolution of these scales is plenty for mixing epoxy. Why should I buy a 500€ scale when a 8.50€ scale does the job?

You can ask how many people fall for (believe) the specs of these scales. That's an entirely different thing.

Cheers  Peter

[magic]

Correction: "resolution" is meaningless if it's not backed by any accuracy

As for the 8068, the worst error I found so far is 3% at 1g, so probably good enough for mixing epoxy, but it is also the case that anything would work.

[Slartibartfast]

Correction: "resolution" is meaningless if it's not backed by any accuracy

As for the 8068, the worst error I found so far is 3% at 1g, so probably good enough for mixing epoxy, but it is also the case that anything would work.

I do not quite understand your first remark, but I suspect I see what you're aiming at. In fact, I'd better used the probably more common word "precision" for what I had in mind (in the old times when analog meters abounded these words were synonyms). Precision is what I need for mixing epoxy, accuracy does not matter, and in fact can be lousy if trueness is bad. If a scale has good precision but no trueness and hence no accuracy, I can still compare weights, and find accurately whether they are equal or not, or which one is larger. If the scale shows both as 1000 tons even they are only 1 gram it does not matter for the comparison.

It is true though that I indeed greatly appreciate that there is not too bad linearity. Without linearity it would be quite cumbersome to mix something like 100:40, but even that could be done.

[mzzj]

What surprises me is that so many fall for these cheap Chinese scales.

What do you mean by that? Who "falls" for those scales? I guess you cannot mean all those who buy them? It is as with other tools: You need to take into account their limits.

I have one. I use it mostly to balance the relative amounts of binder and hardener when mixing epoxy. I do not need a scale with 50000 counts (or whatever it is that mine has), and in particular for that application I do not need any accuracy, just a little resolution! And the resolution of these scales is plenty for mixing epoxy. Why should I buy a 500€ scale when a 8.50€ scale does the job?

You can ask how many people fall for (believe) the specs of these scales. That's an entirely different thing.

Cheers  Peter

I use mine also for mixing epoxy and to cook various chemical experiments. I need hardly ever better than 1% accuracy but mg resolution comes handy time to time.

Unlike the noobs here I checked mine with E2 calibration weight set  :

[magic]

Unlike the noobs here I checked mine with E2 calibration weight set  :

There is a sucker born every minute

[HighVoltage]

What surprises me is that so many fall for these cheap Chinese scales.

What do you mean by that? Who "falls" for those scales? I guess you cannot mean all those who buy them? It is as with other tools: You need to take into account their limits.

I have one. I use it mostly to balance the relative amounts of binder and hardener when mixing epoxy. I do not need a scale with 50000 counts (or whatever it is that mine has), and in particular for that application I do not need any accuracy, just a little resolution! And the resolution of these scales is plenty for mixing epoxy. Why should I buy a 500€ scale when a 8.50€ scale does the job?

You can ask how many people fall for (believe) the specs of these scales. That's an entirely different thing.

Cheers  Peter

Well, that was bad choice of wording on my side.
I meant falling for the ridicules specifications !

For some purposes these cheap scales are perfect and I have a few of them myself.

A few years ago I needed to test lots of Magnets in a cheap way and made a small device to hold a scale and a micrometer with steel plate attached. The adjustment was made that the magnet lost 50% of its weight at the correct setting. Precision was not required and accuracy was good enough with this 200 gram scale.

For this purpose a small China made scale was perfect. See picture


 

[magic]

It gets better: my negative feedback on this item already has two downvotes. As I scrolled down to even find it, I encountered another report of this anomaly from past year, also downvoted.
 

It reminded me of a high school buddy who made money working for a "public relations" company, doing roughly that sort of things. Gotta love those Interwebs.

[thm_w]

It gets better: my negative feedback on this item already has two downvotes. As I scrolled down to even find it, I encountered another report of this anomaly from past year, also downvoted.
 

It reminded me of a high school buddy who made money working for a "public relations" company, doing roughly that sort of things. Gotta love those Interwebs.

Can you link the listing?

[Conrad Hoffman]

I use an old Mettler. The only electronics in it is the light bulb that illuminates the scale of the optical lever. The thing resolves 10 ug and the accuracy isn't a lot worse. Here's a DIY trick for very small masses. Measure a length of good wire and weigh it on a good scale. Now you know the mass per length. Cut pieces as needed. If you start with fine wire you can easily create accurate ug masses. Naturally it should be uninsulated, or magnet wire at worst. You can calculate the error if you know the uncertainty of the cut.

[miegapele]

Bought same scale ~2 years ago. At the time it cost ~15USD. There were like 5 models with 100g/1mg resolution on Ali for that price range. Did extensive research and already then there were reviews for other models that they are rounding. Choose this hoping it will not, but to no avail.
But the scale in general is not good, or I would like it to be better. I have 500g/0.01g resolution scale from 5 years back or so, and that looks very good with like 0.02g repeatability. I sort of expected the same from the new scale, but unfortunately repeatability seems to be around 10mg, so hardly better than 0.01g resolution scale.
Bough another one 500/0.01g scale in 2021. which looks the same. However, that might be rounding, just not that aggressive .
I guess availability of calibration weight sets for $3 made manufacturers do this.

This scale round very aggressively, like X,970 is already rounded to X,997. So, there is easy way to test this rounding. Calibrate scale with 101g pretending to be 100. Then weighting 1g it will show 1.000g exactly, weighting 2g it will show something like 1.998g. But weighting both together you will get something like 2.960g . However if manufacturers were smart and did not round that aggressively it would be way harder to prove.

For multimeters its way easy to gradually increase voltage so maybe it will not happen. But who knows. Most buyers don't know any better, buying cheap AD5584 and cheap multimeter showing 10.000 might be satisfying.
Also for resistance they already round shorted leads to zero. I wonder what  is logic in that implementation.

[miegapele]

This is now a thing in on other scales. Got 10kg scale recently (there is at least two similar variations of it, one with grams in upper right corner and milk, and the one with grams in lower right corner). It weights nicely and seems accurate, but it rounds to every 100g. Rounding is such that anything more than 95g is rounded to 99g and anything more than 97g is rounded to 100g. similarly it rounds down above 100g.

For more, see here
Scale also have calibration, and at least two secret menu, one to set scale capacity, one to set something for (60,120,180), maybe idle timeout, and one to set L00,L01,L02m but not sure what that is.

[AVGresponding]

This is now a thing in on other scales. Got 10kg scale recently (there is at least two similar variations of it, one with grams in upper right corner and milk, and the one with grams in lower right corner). It weights nicely and seems accurate, but it rounds to every 100g. Rounding is such that anything more than 95g is rounded to 99g and anything more than 97g is rounded to 100g. similarly it rounds down above 100g.
(Attachment Link)
For more, see here
Scale also have calibration, and at least two secret menu, one to set scale capacity, one to set something for (60,120,180), maybe idle timeout, and one to set L00,L01,L02m but not sure what that is.

Interesting. I have some with exactly the same form factor, and the larger one definitely operates to 1g resolution, no rounding (beyond mg). It's 5kg max though and not 10kg. The smaller one similarly measures to 0.01g resolution to a maximum of 500g, though I don't have any calibration weights to gauge its accuracy. Weighing parcels before I take them to the Post Office shows the larger one to over-read by a percent or so, haven't had an opportunity to compare the smaller one yet.

[Whales]

My father recently bought a set of $19AUD 3kg 0.1 gram scales off eBay and has found them below promised spec.  Digikey, RS and E14 want hundreds for scales with similar written spec.

(1) There are multiple force sensors under the bed (presumably 4, one per corner) and if you shift your mass around to different positions then you can get more than 1g difference for a ~500g weight.

(2) It does the nonlinear lie trick near 0.0g, so you can't tare the scale and use it to compare similar masses.  The manual states that the minimum mass is 0.3g, perhaps that's what they mean, but it's clearly a software limitation (not a physical one).

Scale also have calibration, and at least two secret menu, one to set scale capacity, one to set something for (60,120,180), maybe idle timeout, and one to set L00,L01,L02m but not sure what that is.

L00, L01, L02 might be calibration coefficients for the individual load cells, assuming it has multiple load cells under different corners of the bed.  If there are three then maybe it only has 3 cells (triangle formation) or perhaps it has 4 and you cal 3 against 1 reference corner (square formation).

[DavidAlfa]

Are you weighting californium? ($27M/ gram)
You can't use whatever scale you want for trading purposes (Precious metals and such), so why is it sh** for a 14mg error?

What the hell do you spect from a cheap Aliexpress scale? https://www.aliexpress.com/i/1005005869570109.html

[miegapele]

L00, L01, L02 might be calibration coefficients for the individual load cells, assuming it has multiple load cells under different corners of the bed.  If there are three then maybe it only has 3 cells (triangle formation) or perhaps it has 4 and you cal 3 against 1 reference corner (square formation).

My 3kg 0.1g scale has only one load cell, so it's not that. This might be some backlight intensity I would guess, but not implemented.
But my scale is quite good, it's repeatable to 0.2g I would say, and has no weight differences wherever you place the weight.

[ebastler]

Are you weighting californium? ($27M/ gram)
You can't use whatever scale you want for trading purposes (Precious metals and such), so why is it sh** for a 14mg error?

I'm confused -- which post are you responding to? One of this year's posts or one of those from two years ago?

[DavidAlfa]

Haha true, I missed the date. Yeah to the original one

[Whales]

L00, L01, L02 might be calibration coefficients for the individual load cells, assuming it has multiple load cells under different corners of the bed.  If there are three then maybe it only has 3 cells (triangle formation) or perhaps it has 4 and you cal 3 against 1 reference corner (square formation).

My 3kg 0.1g scale has only one load cell, so it's not that. This might be some backlight intensity I would guess, but not implemented.
But my scale is quite good, it's repeatable to 0.2g I would say, and has no weight differences wherever you place the weight.

Perhaps they use the same firmware and electronics on a variety of models?

[thm_w]

Are you weighting californium? ($27M/ gram)
You can't use whatever scale you want for trading purposes (Precious metals and such), so why is it sh** for a 14mg error?

https://www.dea.gov/resources/facts-about-fentanyl

[DavidAlfa]

Not an expert in drugs, but that's why you never dose it in its pure form, it's just impossible. 2mg and you're dead.
So you weight 1 gram and mix it with let's say 1000g of another inert substance to make its concentration manageable.
Now, 1mg dose is 1g of product, a slightly overdose of 1.2g won't kill you.
The problem now is in the mixing homogeneity, must be absolutely perfect, or you'll risk taking the "spicy" salt pinch.
Not the scale problem, but the procedure.

Anyways, that's why you don't mess with fetanyl. It's like playing with a 100KV pole and a copper rod, "how close can I get?" LOL.

I got it administered several times during my long stance in the hospital few years back. I must say it's a hell of a drug.
Makes you feel in heaven, forget all problems, like when you were a child and it was the last school day before summer holydays.
Thankfully all I need to keep my mood is some ocassional nachos & bacon!

[cosmicray]

This is also true for calibration weights!
I bought a 1kg calibration weight on ebay a few years ago and it has a M4 set-screw in the bottom. So, naturally I took it out and wondered why there was a screw. Well, I found sand grains behind the screw to adjust the mass of the weight. And this weight was of the F1 class!
Unreal!

I have a couple of very old USPO/USPS manual scales here. They both have calibration adjustments like you describe. Never checked to see of there is sand inside. Both of them have dampening pistons under the bottom, which are supposed to be filled with whatever the manufacturer specified (which I was never able to discover). Seems like I put a thin consistency motor lubricant in them, and they work. The larger of the two is now approaching 60 years of age. Built better than a tank.