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I am interested in getting a very reliable and accurate weight scale that is accurate to the gram.
Not interested in any smart scale etc.
Googling I see some "smart" options and the non-smart ones seem more of the bathroom type scales quality or at least I don't know how to evaluate which one is good.
I am not sure if a question about a recommendation is acceptable here, so I'd ask how can I evaluate if a weight scale is reliable and accurate.

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    As you guessed, we don't give purchase recommendations here. As far as answering how to evaluate if a weight scale is accurate, what kind of scale are you talking about? Kitchen, or bodyweight scale? Sep 7 at 18:43
  • @EricWarburton: body weight scale, but very accurate to the gram granularity. E.g. not just 80.9 but 80.9234 or similar
    – Jim
    Sep 7 at 19:03
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    I'm curious, what are you measuring that you need it to be that accurate? Sep 7 at 19:14
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    Your weight will fluctuate several pounds per day. I average about 4-5 lbs difference in the morning vs the night. This will depend on when food/liquids go in and out of your system. Unless you are planning on weighing every piece of food/liquid that goes into your body, it is completely unnecessary since 99% of the daily changes you experience through a hyper accurate scale will just be measuring your food. It is better to just measure once a week at the same time of day and notice the trends, and adjust your food intake accordingly. Sep 7 at 19:23
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    @Jim It means "build a scale using strain gauges as the measuring sensor(s)." A strain gauge is a mechanism that converts distortion/displacement to resistance, which can then be used to calculate a weight. A commercial 100kg scale w/ 1g reading (which is different yet than 1g accuracy) will likely be fairly expensive. And again--that level of accuracy really isn't going to be particularly helpful. It's two-thousandths of a pound. That's just not useful information. Sep 7 at 20:10
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When looking for a scale you also need to specify capacity. A typical bathroom scale is 150kg, but medical scales are often available to accommodate more massive people.

For the sake of argument, I will assume you need at least 100kg capacity which means with 1g resolution, the scale must have 100,000 divisions. Those certainly exist, but it does require more careful engineering than a consumer scale.

Physicians scales are commonly capable of 100g resolution but I've spotted at least one with 50g resolution. They should meet their specifications on accuracy (typically given in terms of linearity and repeatability,) and precision (normally stated as readability.) As the comments have been saying, your daily weight fluctuations make higher precision of limited use, unless you are performing an experiment and addressing ingestion and excretion of food/water.

However, veterinary scales are available with a greater number of divisions. Unless your subject is small for a human adult, better than 50g is going to be tricky. There are veterinary analytical scales that have 100,000+ divisions but they are focused on smaller lab animals and I haven't seen one above 32kg capacity. Which is unfortunate, because a key feature of veterinary scales is that they average the weight over time to account for the fact that living animals cannot keep still enough to get a steady reading with this much precision being expected.

There are industrial scales with sufficient divisions that they meet the requirements for both capacity and resolution, though one would have to check with the vendor on whether it supports dynamic weighing to allow for fluctuations caused by a living subject.

To touch on a point raised in the comments, you cannot get this level of precision without taking care to eliminate sources of error. The scale needs to be placed/installed per the manufacture's specifications with regards to being level, a stable foundation to avoid problems with vibration, and temperature stability. Some scales have internal calibration masses, but external calibration with 1 or more precision masses is not uncommon. You might find a new scale for less than $1000 that just squeaks by your requirements, but $2000-$4000 seems more likely. Relaxing the precision mandate will make it much more affordable.

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  • The IPF uses a fancy scale which is within 20g. Beyond that, I agree, you're looking in the legal-for-trade area and any of those scales that can weigh 150kg at ±0.001kg are going to be north of $15k USD.
    – C. Lange
    Sep 7 at 22:11
  • I don't actually need "at least 100kg" capacity. But at most "100 kg capacity". I.e. nobody weight is over 100kg. Also no it would be way over 32kg
    – Jim
    Sep 8 at 6:51
  • @Jim Cheapest I found that claims 1g accuracy @ 100kg is $4500, and I’m skeptical they mean accuracy (as opposed to reading). It’s still not clear what you think you’ll be measuring—if the goal is to target metabolic processes it’ll be opaque and inaccurate. I don’t see any way to understand what’s noise vs. meaningless data—1g at 150lbs is like 0.001% of the weight. That kind of accuracy, where a heartbeat will cause fluctuation… again—what is the purpose? Sep 8 at 11:39
  • @DaveNewton: I didn't think that it is so complicated. I am interested in keeping a log for daily changes of weight to avoid weighting e.g. 4 weeks to see the variation in a usual bathroom scale. Since it is non trivial, what would be the best option for an accurate digital scale? E.g. I have one currently that does not seem to have anything to change the calibration if the weight is off (perhaps too cheap)
    – Jim
    Sep 8 at 12:27
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    @Jim It is for convenience, because then I don't have to do any math myself (or only once in code, anyway). I don't know if they're "more reliable" outside of the same "more $ tends to be more accurate/reliable" matrix. It sure seems like you're over-thinking all this. Just buy a scale. Sep 8 at 14:55

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