# Flipping Scales



## 4085 (Nov 23, 2012)

I have several sets of scales, from cheap to reasonably expensive, and the ALL give different readings. In addition, if I weigh a pf, then move its position on the scale, I get a totally different result. For example, just made a shot, put the pf on, fared it, put some coffee in, checked the weight, put some more in and it read the same weight, changed the position slightly on the weighing platform and it changes significantly! Is there a fool way of actually believing what is in front of our eyes?

I have a set of tare weights and again, they produce a different result on nearly every set of scales. Please, all of you, if you have more than one set of scales, compare [email protected]


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## garydyke1 (Mar 9, 2011)

I have 4 different scales in front of me and have a handful of beans

scale 1 - 19.66g

scale 2 - 19.66g

scale 3 - 19.7g

scale 4 - 19.66g

however a hot portafilter basket straight out the machine

scale 1 - 35.98g

scale 2 - 35.99g

scale 3 - 36.0g

scale 4 - 36.09g

!!!

the reading is changing whilst it cools down


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## 4085 (Nov 23, 2012)

Interesting Gary, but what I am suggesting, is put something onto the weight platform, then change its position around the weigh platform. Do you still get a uniform result?


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## The Systemic Kid (Nov 23, 2012)

Wonder how many forum members own a tare weight?


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## ahirsty (Jan 9, 2014)

The scales I use for measuring my shot output changes depending on if I'm touching the machine or not...


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## Neill (Jun 26, 2013)

The heat from a hot chemex always affected my kitchen scales. I put a cork mat on it. Doesn't happen with the bonavita but there's a drip tray on top of it.


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## Dylan (Dec 5, 2011)

garydyke1 said:


> I have 4 different scales in front of me and have a handful of beans
> 
> scale 1 - 19.66g
> 
> ...


Evaporating water I guess!


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## The Systemic Kid (Nov 23, 2012)

dfk41 said:


> Interesting Gary, but what I am suggesting, is put something onto the weight platform, then change its position around the weigh platform. Do you still get a uniform result?


Think that's where, 'you get what you pay for' comes in David. Got two sets of 14cm x 14cm platform scales as well as jewelers' scales and they all weigh accurately across the area of the platform using a tare weight.


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## 4085 (Nov 23, 2012)

Patrick, I bought a set of £40 scales, the ones they were doing at the London Coffee gig, cannot remember the name now. I would expect them to be accurate. i agree with the cheaper ones. Tare weights were a couple of quid off Ebay!


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## Phil104 (Apr 15, 2014)

The Systemic Kid said:


> Wonder how many forum members own a tare weight?


 Not me but I do have access to a number of 20p pieces at 5gm a piece.


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## 4085 (Nov 23, 2012)

http://www.ebay.co.uk/itm/261516023983?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT


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## Phil104 (Apr 15, 2014)

Blimey... all too instantly affordable. It's hard to imagine how they can be produced and posted for this price. Presumably, they are accurate.


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## Phil104 (Apr 15, 2014)

Just ordered some and look forward to playing with them and using my 20p pieces in the parking meter.


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## ronsil (Mar 8, 2012)

I use those for calibration. They just lack a 100g weight which I bought separately.

May have to wait???? a bit for postage from Far East


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## 4085 (Nov 23, 2012)

Now there is a thought Phil, about accuracy! I still maintain that if you move your item to be weighed around the platform, unless I am genuinely unlucky, the results are different!


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## Gangstarrrrr (Mar 4, 2013)

D_Evans said:


> Evaporating water I guess!


More likely the heat is impacting the weighing pad, making in expand and then contracting as it cools.


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## hotmetal (Oct 31, 2013)

I have 2 scales and "luckily" one measures to 1dp, the other 2dp. This means I can rationalise the delta by attributing it to rounding error.

I've noticed this business with moving and cooling having an effect, though only on the 2dp scales (which also have a bigger platform). I think it's to do with the way the scales work, which I believe is some sort of 'strain gauge' principle where the electrical resistance of the load cell is affected by the pressure on it. The positional error could be due to the weight acting unevenly on the platform, and I attribute the heat error to the resistance being affected by the temperature (a known factor in load cells using Wheatstone bridges), which translates into a false reading of the mass.

On the other hand, I could have pulled that out of my, er, hat.

Are flipping scales for weighing flying pancakes?


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## DavecUK (Aug 6, 2013)

David,

The larger the scale platform the more variance you are likely to get as you move things around....best to go for scales with the smallest platform possible. Also the heavier the weight (compared to the max of the scales) the more likely variance is to show. In all cases always try to put the object being weighed in the same place each time. If you use a specific container for weighing materials that is even better. Also some of these cheap scales have very high weight limits, but quite flimsy construction again more cause for variance as the weight weighed goes up.

I have a set Kern of Retail scales that weigh up to 3Kg accurate to 1g and have little or no variance wherever objects are placed on the platform (and for all weights up to their limit)....but they cost £300+....so you get what you pay for...and of course they are no use for espresso weighing.


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## 4085 (Nov 23, 2012)

Pancakes, I will try them! The scales seems to be daily accurate using the tare weigh which is a maximum individual weight of 50 gms. My better scales weigh 50.1 in the centre and 50.2 around the edges. I will find a cool pf shortly and try something a bit heavier.

I did wonder if the scales that did not have a separate weighting platform might be inherently more accurate. It must be possible for dirt, liquid, coffee etc to get lodged underneath?


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## hotmetal (Oct 31, 2013)

My 2dp scales are the £7 Chinese ones off the bay, so I don't have great expectations of them but they're actually alright (for my level anyway!)

I tend to let the shot run into a shot glass, and use the plastic cover of the scales upside down as a drip catcher to stop the occasional spritzer knackering my <irony> precision instrument </irony>. Whether this provides any thermal decoupling and load spreading is open to debate but seems to be, on the whole, a Good Thing.


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## gman147 (Jul 7, 2012)

Would imagine tolerance levels of between +\- 10%

If they offer more accurate tolerance then you're gonna pay considerably more.


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## jeebsy (May 5, 2013)

Quite funny people will spend £2k+ on precision machines and grinders then go for bargain basement/piece of shit scales (although they just need to 'do a job'). Would love some Ohaus but would need to have a lot of spare cash before I could justify them.


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## MWJB (Feb 28, 2012)

gman147 said:


> Would imagine tolerance levels of between +\- 10%
> 
> If they offer more accurate tolerance then you're gonna pay considerably more.


Decent scales will have tolerances published, even cheap scales should be much better than +/-10% of max weight, but if you have more than one set/a calibration weight you can test yourself for accuracy & precision.


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## garydyke1 (Mar 9, 2011)

D_Evans said:


> Evaporating water I guess!


no, the basket was dry


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## Dave.wilton (Dec 24, 2012)

jeebsy said:


> Quite funny people will spend £2k+ on precision machines and grinders then go for bargain basement/piece of shit scales (although they just need to 'do a job'). Would love some Ohaus but would need to have a lot of spare cash before I could justify them.


Surely the accuracy does not matter so long as the repeatability is good? What does it matter if I'm weighing in 17.5g and it's actually 18g so long as I'm weighing in 17.5 every time.

I ensure this by using the same container to weigh beans into. It weighs 5.4g. I put it on, check it weighs 5.4g. tare, add my beans and then tip them out. If the scale doesn't weigh -5.4 at the end something went wrong


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## DavecUK (Aug 6, 2013)

Dave.wilton said:


> Surely the accuracy does not matter so long as the repeatability is good? What does it matter if I'm weighing in 17.5g and it's actually 18g so long as I'm weighing in 17.5 every time.
> 
> I ensure this by using the same container to weigh beans into. It weighs 5.4g. I put it on, check it weighs 5.4g. tare, add my beans and then tip them out. If the scale doesn't weigh -5.4 at the end something went wrong


you are completely correct...but i think the issue originally raised, was one of repeatability.


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## gman147 (Jul 7, 2012)

Repeatability is important yes, but the purpose of scales is suppose to accurately weigh things. Defeats their purpose if they tell you the incorrect weight of something.


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## charris (Feb 17, 2014)

There is another problem that I have noticed: When I place the Hario scale on my Classic's drip tray and start the brewing sometimes it will immediately add a few grams even though there is no coffee yet in the cup - this is a vibration problem and the Hario seems to be affected by this. What I do is I immediately tare again but it is a problem because you cannot always be that alert to tear the scale again and again and sometimes the vibration can add immediately 5g or so...


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## MWJB (Feb 28, 2012)

There are usually parameters for repeatability and accuracy. If they're a little out then it's better that they're a little out by the smallest amount each time, rather than out by so much, then giving a different reading by as much again. I'd guess the weights are more repeatable than accurate, in most cases.

e.g. Accuracy for 0.1g (readability...the fact they have a given number of decimal places doesn't mean that they are accurate to each readable digit shown) scales might be +/- 0.3g, but repeatability/precision might be +/-0.1g.

You want the scales to show the least deviation of weight to that applied each time you weigh.


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## MWJB (Feb 28, 2012)

gman147 said:


> Repeatability is important yes, but the purpose of scales is suppose to accurately weigh things. Defeats their purpose if they tell you the incorrect weight of something.


Their purpose is to give you a reasonably accurate weight reading, given cost, reasonable expectation, reaction time etc.

If you're buying £5 0.1g (readability) scales and expecting them to be accurate to 0.1g with total repeatability, you're being a bit optimistic. It's a question of determining what level of accuracy is meaningful given the application. If in doubt go for greater readability, though this will often mean a lower max weight.


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## gman147 (Jul 7, 2012)

Was I? Where. I was merely stating the function of scales. I use cheap ass Chinese ones. They weigh accurate enough for me and they repeat accurate too. They cost me about £3.

I was pointing out that accuracy is important to the other chap who stated Repeatability is only important.


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## MWJB (Feb 28, 2012)

gman147 said:


> Was I? Where. I was merely stating the function of scales. I use cheap ass Chinese ones. They weigh accurate enough for me and they repeat accurate too. They cost me about £3.
> 
> I was pointing out that accuracy is important to the other chap who stated Repeatability is only important.


Sorry, "you're being a bit optimistic" was meant as a general turn of phrase, meaning people generally rather than a criticism of you personally.


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## gman147 (Jul 7, 2012)




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## Pompeyexile (Dec 2, 2013)

I just put my basket on the scales, then turn them on and they automatically read zero and I add my ground coffee until they read 18g. I do the same for the whole bean 36g. Even though I can tar I don't bother. Should I, does it make a difference?


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## Phil104 (Apr 15, 2014)

Unless I have missed the point, it sounds like what you are doing, you are doing it consistently and if you like the output - then why not? At the same time it depends on how you are measuring the output because you aren't starting with 18g of ground coffee in your basket - it's obviously going to be 18g-weight of basket so any calculations about time, weight or volume of shot will be affected. But... if you are enjoying what you are making, why break it?


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## dsc (Jun 7, 2013)

Bigger platform scales might still have a single smallish load cell in the middle of the platform (especially cheap ones). What this means is that anything bigger which has it's weight center outside of the middle of the platform will probably not indicate correctly. Get one of those cheap £5 scales and take them apart, you'll see what I mean, they are more accurate the closer the weight center of the weighed item is to the center of the platform. Irregular shapes and odd weigh distribution will throw them off and you'll get readouts which don't show the true weight of the item. More precise scales have four load cells in the corners (or more spread out) and there's some fancy averaging going on to get a true weight reading.

Also as already mentioned insulate hot items as it warms up the platform / loadcell and affects the readings.

T.


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