Weights and weighing machines
Weighing scales, digital balances, jewellery scales, pocket scales and approved balances for diamonds, gemstones, jewellery, scrap, coins and bullion.
I sometimes refer to weighing machines as 'scales' and sometimes as 'balances' - today both words mean exactly the same.
THE BASICS: CAPACITY AND RESOLUTION
The readability (resolution) is the finest weight on the display of a digital balance, or the finest divisions marked on a spring balance; the capacity is the maximum weight. Some models read down to ('have a resolution of") 0.001g, some models read down to ("have a resolution of") 100g...and anything in between. The resolution most-used for jewellery, scrap and coins is 0.1g (and the capacity anywhere from 100g to 8000g)
Some people are easily confused by decimal points, e.g. 0.001g, 0.01g, 0.1g etc. Before ordering please do think for just a second:
0.001g = a piece of paper the size of a pin head
0.01g = a small staple
0.1g = a couple of small matches
1g = two or three small paperclips
10g = a one pound coin (actually 9.5g)
100g = nearly half a pack of butter, a large chocolate bar (not a 'giant' bar)
1000g (1Kg) = a small bag of sugar or two small packs of pasta
10000g (10Kg) = a suitcase packed for holiday
- For weighing diamonds. Switch the scales carat (100 points = 1 carat, 20 carat = 1 gram). Whether you get an accurate (true) reading to the nearest 1 point will depend on the quality of the scales. If you pay £20.00 or £30.00 unlikely. If you pay about £50.00 they will probably be OK. If you pay closer to £100.00 they should be good.
- for testing diamonds and gemstones using the specific gravity (relative density) method, see our specific gravity tester for gemstones.
- outside of the jewellery trade, 0.001g is for scientific applications, you really do not need to weigh down to this level for everyday purposes.
- For weighing gemstones, powder for ammunition, checking gold coins to see if they are genuine, see our specific gravity tester for gemstones.
- for weighing gold. To see the price of 0.1g of 9ct gold, click here - then select from the three drop-down boxes on the top left: GOLD, GBP and g. Multiply the answer (far top left) by 0.375. This is the price of 0.1g of 9ct gold. This is the 'middle' (the 'official') price, you will never get this much when selling scrap, you will never pay this little when buying jewellery, full details in The Gold & Silver Buyer's Handbook.
- for other precious metals, platinum and Palladium
- silver isn't so valuable so you can get away with a resolution of 1g, but if you buy a high-capacity 0.1g balance, you can use it for gold and silver.
- for checking the weight of coins to see if they are genuine, look up the weights of coins in The Gold & Silver Buyer's Handbook (if the coin is the wrong weight, it is not genuine).
- catalysts for adhesives; photographic chemicals; medicinal herbs; eggs (to see which are likely to be fertilised); rare foods (some mushrooms, truffles, saffron).
Other factors to consider when buying a 0.1g gold scale:
- the physical size. Must it be pocket-size? Or might you be weighing teapots and salvers? Or maybe something in between that will take jewellery from small earrings to large bangles.
- the price. Low-capacity scale are (with the 0.1g resolution) cheap, e.g. you can get tiny 100g / 0.1g for about £5.00. If you want the same 0.1g but up to 3000g, then aim to spend £30.00 to £50.00. Once you want 0.1g up to 5000g or 8000g the price starts creeping up towards £100.00.
- For weighing silver. To see the price of 1g of Sterling (-.925) silver click here - then select from the three drop-down boxes on the top left: SILVER, GBP and g. Multiply the answer (far top left) by 0.925. This is the price of 1g of Sterling silver. This is the 'middle' (the 'official') price, you will never get this much when selling scrap, you will never pay this little when buying jewellery, full details in The Gold & Silver Buyer's Handbook.
- for the bulk-counting of coins (110g of silver coinage has a face value of £1.00)
- for letters, packets and parcels.
- for food.
There are two ounces. The Ounce Avoirdupois (often called the "English Ounce") = 28g and is for weighing food and goods; the Troy Ounce, ozt = 31.1g and is for weighing precious metals. The Pennyweight (20 dwt = ozt) was discontinued, here in the UK, over 30 years ago but is still used in the U.S.A. The sub-division of the pennyweight was the grain (gr, originally based on a grain of wheat) and is still used for weighing powder for ammunition. A carat (metric carat) is 0.2g, used for weighing diamonds (divided into 100 points, pts) - not to be confused with carat as a measure of purity (spelt Karat in the U.S.A.). See a conversion chart, useful for weighing gold and silver. Or there's a conversion chart that will convert dozens of different weighing systems.
MECHANICAL OR DIGITAL?
Mechanical balances with springs (spring balances) are out of fashion, people tend to think that any machine with batteries and an LCD display must be accurate, and anything purely mechanical isn't so accurate. Not true, a good quality spring balance is every bit as accurate as a digital balance (see below for definition of 'accuracy'). The high precision PESOLA spring balances are smaller (thin and long) than any digital balance, battery-free, difficult to overload, and survive being dropped.
Spring balances are the best choice for hanging (with a clip or a hook) letters and small packets, or bulky items such as silver teapots or bags of silver scrap.
The pocket-size digital balances are best for tiny object such as rings, earrings, rare coins, especially if you intend to carry it around. The larger, table balances, should be chosen for fixed use on a workbench or table. Both are available in a large range of resolutions and capacities.
APPROVED FOR USE IN TRADE
If you buy or sell on a weight-for-value basis you must, by law, use an approved balance. "Approved" means approved by Trading Standards. We do sell approved digital balances. An approved balance must be used whether selling (or buying) in a shop, antiques fair, street market, boot sale or even from home. Even auction houses must use approved balances, even though, technically, they are not 'buying and selling." See the QUICKTEST article explaining approved balances.
If it is a tube with a spring we call it a spring balance (they weigh down to about 1g or down to about 0.1g). One variation is a 'digital spring balance' - you hang the item on the hook and read a digital display (it works by deforming plates of metal rather than stretching a spring, but the principle is the same). A variation is a semi-circle of metal with a hook and a loop (no springs), popular as a letter balance. A good name to describe all these is 'hanging balance'.
If it is flat-ish and has a battery and a digital readout and sits on a table (many are small enough to fit in a pocket) we call it a digital (or electronic) balance. Since these have flat weighing platforms, they are sometimes known as 'platform balances', as opposed to digital 'hanging balances' (like a spring balance but with a digital display).
Technically-speaking none of the above are 'balances' at all, it is only a balance if you 'balance' the goods against weights, e.g. two weighing pans balance over or under a beam (a beam balance)...which we don't sell.
- Readability (resolution) and accuracy
Put a 100g. weight on two digital scales, you might get two different readings, both have the same readability (resolution) but one might be more accurate than the other.
Nothing is 100% accurate.
Accuracy is measured in 'percentage'. Multiply the percentage by the weight (any weight you like, any weight you are likely to weigh) to calculate the possible error. I've never been able to find out the percentage accuracy of the miniature digital scales used in the antiques trade, but from my experience of manufacturing them many years ago, I would guess it's about 0.1% for low-cost (under £100.00) scale, 0.01% for an expensive (over £300.00) scale.
An example. You weigh 10g, the calculation is 10 X 0.001 = 0.01g possible error. On a scale with a resolution of 0.1g. you would never notice an error of 0.01g. But now try a heavier weight and you will see that the error is noticeable, e.g. if you weigh 3000g the calculation is 3000 X 0.001 = a possible error of 3g. There's no point in complaining that at 3000g the scale reads 2997g (or maybe 3003g) because this is simply the accuracy you will get with a low-cost scale.
In practice, it's not that bad. Even the cheaper (under £100.00) balances can often (and with careful calibration - see below) weigh 3000g and get a reading of 3000g ±1g. This is technically, quite impressive...but it is not guaranteed. Basically, the more you pay, the better the accuracy, you would not expect the same accuracy on a £20.00 balance as you would with a £450.00 balance. Be wary of very cheap balances (e.g. under £10.00), if they become inaccurate (and if you cant fix them by recalibrating, see below) dont struggle, throw them away and buy something better.
The reading on a measuring device (any measuring device, e.g. thermometer, weighing machine, clock...anything) must match the units it is measuring (e.g. degrees, grams, minutes). This matching-up is called calibration. Electronic machines go out of calibration, it is the nature of electronics. Most can be recalibrated. In the scientific industry all machines need to be recalibrated regularly (usually once a year), a technician will call to do this, the charge is about £100.00. But nobody is going to spend£100.00 to recalibrate a scale that costs £20.00.
Nearly all balances include calibration instructions which involve pressing buttons in a complicated sequence and placing a weight (or sometimes two weights) on the weighing platform. But the weight is never included when you buy the balance. I would suggest buying a weight when you order buy the balance, they are not expensive and buying the balance and the weight together will save on postage. There is an article about calibration.
For more details about calibration (and how to calibrate your balance) click here.