Approved weighing scales for 'use in trade' - buying precious metals by weight

Two models by Ohaus, 620g / 0.1g model (SJX622M)  or 1500g / 0.1g (SJX102M)

In this article I refer to Weights & Measures Inspectors. These are Trading Standards Officers who happen to deal with weights and measures. Up until now (Summer 2025) they have concentrated on shops, now they are focussing on fairs, markets etc. 

SUMMARY

Use in trade means buying on a value-for-weight basis (a price per gram). This applies no matter where you use the scales; this applies even if you don't regard yourself as a trader.  

A Weights & Measures Inspector will notice if you are buying by weight, even if you pretend otherwise. He can see whether you are calculating a price based on weight or if you are calculating the price by carefully evaluating gemstones and hallmarks.

You can also use approved scales for selling by weight, but only if the customer can see the display. 

DETAIL: WHO NEEDS AN APPROVED BALANCE?

If you buy or sell by weight (i.e. an amount of money per gram) then you are using the balance 'in trade' and it must be approved. However, if you use it as part of your valuation but do not base the value on weight (e.g. jewellery where the main value is in gemstones, diamonds or antique value) then you do not need an approved balance - you are still a trader, but you are not using it 'in trade', there is no need to read on.

You are using a balance 'in trade' if you are buying by weight, no matter where:  pawnbroker, auction house, shop, unit, centre, kiosk, antiques fair, market, boot sale, local church hall...  You are using a balance 'in trade' even if you don't regard yourself as a trader. 

In the past we said that auctions were an 'iffy' area. Following a 2½ hour meeting with a Weights and Measures Inspector, We can now clarify the position: an auction house must use an approved balance if the item description includes the weight. 

You may say to yourself, "But nobody uses an approved balance in my market, and there has never been a problem." Maybe everyone unloading at the market parks on a double yellow line and there has never been a problem. I can only tell you about the law, not how it is enforced.

WHO 'APPROVES' THE BALANCES & WHO ENFORCES THE LAW?

The actual standards for Weights and Measures are determined by the National Measurement Office who study the law, look at the science, and issue guidelines to Weights & Measures Authorities. The law is enforced by Weights and Measures inspectors, they work for the Trading Standards department at your Local Council. You can find them by going to Trading Standard's Home Page (enter your postcode in the box at the top and click 'go'). If you wish to study the law yourself, see the Weights & Measures Act 1985 and its many amendments. Then, if you disagree with an inspector, you may accept his offer to have the matter settled in court. Of course, Brexit has caused many complications, see the latest information (proposed new regulations 2024).

APPROVED BALANCES, CLASSES OF BALANCE

First, the easy bit. A weighing machine used in trade must be stamped with a special sticker. These stickers are seals that are carefully placed over vital screws on the balance, if you break the seal it will no longer be approved.

There are four Classes (grades) of approved balance:

• CLASS 4 need not concern you, it is for heavy items such as heavy goods vehicles
• CLASS 3 need not concern you, it is for general goods, e.g. food (anything from small packets of herbs to big bags of fruit)
• CLASS 2 is for items that have a high value per gram, specifically precious metals. 'Precious metals" are gold, silver, platinum and Palladium.
• CLASS 1 need not concern you, it is for scientific applications, e.g. for weighing down to 0.0001g

THREE COMPLICATIONS

- Complication No. 1: 1g or 0.1g or 0.01g?

The balances we sell can be used in trade (for buying by weight) to the nearest 0.1g. Beware when buying from other suppliers, that the resolution displayed on the scale may not be what is permitted for 'use in trade'.

When you buy an approved CLASS 2 balance the manufacturers might give you its specification as, for instance, 6000g in steps of 0.1g. What they don't tell you is that once it's approved, you are not supposed to use that last decimal place when used "in trade". So, for instance, having spent hundreds of pounds and thinking you will be weighing down to 0.1g you will discover that the balance now has a red cross painted over that last decimal place so that it only reads to the nearest 1g. (though the 0.1g will still be visible under the red cross). For your own purposes (away from customers, for your own valuation purposes) you may weigh to 0.1g, but when buying by weight you are supposed to ignore the 0.1g and work to the nearest 1g.

If you are selling by weight, the customer must be able to see the display and you must never use a balance with a "crossed out" digit.

Why so complicated?? - because when the law was made, it was assumed that retailers sold goods by weight (mostly groceries) but it never occurred to the law-makers that a trader might buy by weight, and so the words "and buying" were not included in regulations.

- Complication No. 3: balances calibrated by area

Some CLASS 2 balances are calibrated for a particular area (usually a town, sometimes a full postcode). This is to allow for variations in gravity. So if, for instance, you use a balance in central Liverpool, then it will be calibrated for central Liverpool, you can't legally use it anywhere else.

We have found a simple solution to this. We no longer sell this type of approved balance. Our approved balances can be used anywhere.

HOW OFTEN DOES AN APPROVED BALANCE NEED TO BE CHECKED?

Check your balance whenever it is moved. If you work at fairs and markets, that includes moving to a new venue, it also includes moving the balance from one side of the stall to the other. Even if the balance lives on a shop counter and is never moved (not even by a few inches) it is wise to check it every few weeks.

To check it, buy a weight, any weight that is near (or at) the top of the balance's range. Switch the balance on, place the weight on the platform, check the reading. It really is no more complicated than that.

CALIBRATION

Do not confuse 'checking' the scale with calibrating it.

Calibration means matching an physical (very accurate) weight with the electronics.  The calibration weight is sealed inside the scale and operated by pulling a lever. The process is very simple, hold down the TARE/MENU button until you see "Menu", release the button, press "Yes", follow the instructions on the screen, the entire process takes 30 seconds. 

It is good practice to calibrate them:

• at the start of each day
• each time you switch them on
• the temperature changes greatly. For instance, if it’s 14° first thing in the morning and  23° once the shop/hall has warmed up, calibrate them each time you use them until the temperature has stabilised.

It is essential to calibrate them if:

• they aren’t weighing correctly (use a test-weight, it need not be very accurate, just entire you get the same reading each time). 
  
• they are moved from one location to another (e.g. town, suburb, shop).
• they are moved from one place to another in the same location (e.g. from the shopfront to the office, or from one table in a hall to another)
  

If you have an inspection and the scale is not reading correctly, the inspector will 'cancel' the approval markings and you will no longer be permitted to trade. The inspector will not calibrate the scale for you!  You must keep it calibrated.