Calibrating a price computing scale has two parts: test the weight with certified test weights, then check that the scale multiplies that weight by the unit price correctly. Under OIML R 76, the price to pay must equal the displayed weight times the unit price per kg or per 100 g, rounded to the nearest price step. Test the weight first, because a weighing error flows into every bill.
A counting scale needs the same weight test plus a hand-counted sample. In India, a scale used to sell goods also needs Legal Metrology verification, and a shop's own check does not replace it.
How price computing and counting scales work
A price computing scale shows three numbers: the weight, the unit price you key in and the price to pay. OIML R 76 restricts the unit price to a price per kilogram or per 100 g. When the scale prints a ticket, the ticket must show all three numbers.
A counting scale works out how many identical pieces sit on the pan. It weighs a sample, divides by the number of pieces to find the weight of one piece, then divides the total weight by that figure. On the Ace JS-6002, you press the counting key, place the number of sample pieces the display asks for, confirm and add the rest. Piece counting is also built into the Ace KN 10 kg weighing scale, which reads 10 kg in 0.5 g steps.
The sample is the weak point. If the sample pieces are lighter or heavier than average, every count after it is off by the same proportion. A bigger sample spreads that error across more pieces, so count 20 or 50 pieces rather than 5.
What OIML R 76 asks of a price computing scale
OIML R 76 is the international recommendation for non-automatic weighing instruments. Its rules for scales used in direct sales to the public include these:
- Both sides see the numbers. Weight, unit price and price to pay must show to the vendor and the customer at the same time. Digits shown to the customer must be at least 9.5 mm high.
- No hidden tare. Automatic tare is not allowed, and the customer must be able to see when a tare is in use.
- Rounded to the nearest step. The price to pay is weight times unit price, rounded to the nearest interval of price to pay.
- Numbers stay on screen. The three values stay visible for at least 1 second once the weight settles, and for no more than 3 seconds after the load is lifted.
- Tickets match the display. A printed ticket shows weight, unit price and price to pay, and the printed and displayed values may not differ at all.
Test weights you need
Use certified test weights, not stones, coins or sealed packets. OIML R 111 names class M1 weights for use with medium accuracy class III scales. A 10 kg M1 weight may be off by no more than 0.5 g, and a 1 kg M1 weight by 50 mg.
A 30 kg scale that reads in 5 g steps has 6,000 steps, which puts it in class III under R 76. Omace's Om-TT shop scales sit in this group: the series is a Legal Metrology approved model, and its approved 30 kg model is approved in accuracy class III with e = 5 g and Min 100 g. R 76 also says a test weight's error must not exceed one third of the scale's permitted error at that load.
You do not always need certified weights up to full capacity. Under the Legal Metrology (General) Rules as amended in July 2026, a scale tested at its place of use may carry any steady load for part of the test, provided certified weights make up at least half the capacity. That share falls to one third when repeat readings agree within 0.3 e.
How to check the weight and the price, step by step
- Set up. Place the scale on a firm, level counter away from fans and drafts, switch it on with an empty pan and wait for 0.
- Repeat one load. Put the same weight on three times. The readings should differ by no more than the permitted error for that load.
- Test across the range. Load about a quarter, a half and all of the capacity, and note each reading against the weight.
- Test the corners. Place about one third of the capacity on each quarter of the pan in turn, as R 76 does in its off-centre test.
- Test tare. Put an empty tray on, press TARE, then add a weight. The net reading must match the weight within the same limits.
- Test the price. Key in a round unit price such as ₹80 per kg and place 2 kg on the pan. The price to pay must read ₹160. Repeat with a weight that gives paise to see how the scale rounds.
- Compare every display. The customer display, your display and the printed ticket must show the same numbers.
If the weight passes but the price is wrong, check the rate and the rounding setting; the calibration is fine. If the weight fails, every price will be wrong in proportion, so fix the weight first.
How much error a shop scale may show
OIML R 76 states the maximum permissible error in multiples of e, the verification scale interval printed on the nameplate. The limit in service is twice the limit at first verification. For a 30 kg scale with e = 5 g, the limits are:
| Load | At first verification | In service | In-service limit at ₹100 per kg |
|---|---|---|---|
| Up to 2.5 kg | ±2.5 g | ±5 g | ₹0.50 |
| 2.5 to 10 kg | ±5 g | ±10 g | ₹1.00 |
| 10 to 30 kg | ±7.5 g | ±15 g | ₹1.50 |
| Corner test, 10 kg on each quarter | ±5 g | ±10 g | ₹1.00 |
At ₹100 per kg, the 15 g in-service limit on a full 30 kg load is worth ₹1.50 per sale. A scale that drifts past it costs either the shop or the customer on every weighing.
Your own check versus Legal Metrology verification
A shop's own check catches drift between inspections; it does not make the scale legal for trade. Section 24 of the Legal Metrology Act, 2009 requires every weight or measure used in a transaction to be verified before use. Section 33 sets a fine of ₹2,000 to ₹10,000 for using an unverified one, and up to one year in prison with a fine for a repeat offence.
An electronic shop scale is re-verified every 12 months. Rule 27 of the Legal Metrology (General) Rules, 2011 sets 24 months for weights, beam scales and counter machines and 12 months for every other weight or measure. A repaired scale cannot be used until it has been re-verified and stamped.
OIML R 76 requires the calibration adjustment on class II, III and IIII scales to be sealed; only class I balances may leave it open. Opening that seal on a stamped scale means a fresh verification. Since 1 May 2026, Section 23 requires anyone who repairs weighing instruments to hold a registration certificate from the Controller of Legal Metrology, in place of the earlier licence.
The wider rules are in the Omace guide to the legal for trade weighing scale, and the general method is in how to calibrate a digital weighing scale.
Common mistakes at the billing counter
- An old rate. The scale weighs correctly but charges yesterday's price per kg.
- Tare left on. The last customer's tray stays tared and cuts the next weight.
- Something touching the pan. A bag edge, a hand or the wall takes part of the load.
- A fan or AC blowing on the pan. Moving air pushes the reading around on small loads.
- A small counting sample. Five pieces set the piece weight for a count of 500.
- A ticket that does not match the display. R 76 allows no difference between a digital display and its printer.
Customers who suspect short weighing can call the Department of Consumer Affairs' National Consumer Helpline on 1915 or message +91 8800001915.
Omace shop scales for the counter
Omace has no billing or price-computing scale yet. Its Om-TT shop scales weigh and tare but do not compute price, so a price check on them ends at step 5. Each has a stainless steel pan, a green LED display that the customer can read and a built-in battery with about 2 days of backup. Every Om-TT scale leaves the Bagru factory verified and stamped by Legal Metrology, so its calibration is sealed from the first day and only a registered repairer may adjust it.
- The Omace Om-TT-Mini SPR double display weight machine weighs 20 kg in 2 g steps or 30 kg in 5 g steps and costs ₹2,500 including GST (October 2026).
- The Omace Om-TT-Running SPR 30 kg weight machine reads 30 kg in 5 g steps on a 240 × 300 mm pan for ₹3,000.
- The Omace Om-TT-ECO kirana weighing machine weighs 10 kg in 1 g steps or 20 kg in 2 g steps for ₹2,200.
The full range is in weighing machines for shop. For a 30 kg counter scale, see how to calibrate a 30 kg kanta.
Omace Brands Private Limited has made and supplied weighing scales in India since 1994 from Bagru, Jaipur. Every Omace scale is checked before dispatch, and store purchases carry a 2-year warranty on manufacturing defects. More about Omace. Omace scales are made in India. As a manufacturer, Omace Brands Private Limited holds ISO 9001:2015, ISO 13485:2016 and EU MDR quality certificates, and CE and US FDA compliance certificates; each is listed with its certificate number on the Omace certificates page. Omace shop, platform, chicken and crane scales leave the Bagru factory verified and stamped by Legal Metrology.
