Average Quantity System

This Topic Includes:
What is the average quantity system?
Compliance
Responsibilities of packers, importers and retailers
Checking systems and sampling
Weighing and measuring equipment
Reference tests
Examples table
Statistical sampling and tolerancies table
MAPSS Officers visits
Glossary

If you are a retailer, packer or importer of packaged goods this topic applies to you. It will provide you with information about the system used by Measurement and Product Safety Service Officers (MAPSS Officers, also known as Inspectors of Weights and Measures) when they carry out quantity checks on most packaged goods. It is known as the Average Quantity System (AQS).

What is the Average Quantity System?

The Average Quantity System controls the net weight, measure, or number of constant quantity packaged goods. It consists of three 'rules'. (See 'Glossary' for definitions of words and phrases used in the rules.)

Rule 1

The actual contents of the packages in a lot must not be less, on average, than the stated quantity.

Rule 2

No more than 2.5% of the packages in a lot may be non-standard. A package is non-standard if the quantity is less than the stated quantity on the package by more than a tolerable deficiency (T).

Rule 3

There must be no inadequate packages. A package is inadequate if the quantity of goods is less than the stated quantity on the package by more than twice the tolerable deficiency.

You should note that 'catchweight goods' are not subject to AQS checking procedures. They are treated as individual packs.

Compliance

One way to comply with these new rules is to pack so that you know all your packages contain at least the stated quantity. Or you may devise a system of checks to ensure that all your packages meet the three AQS rules. This may incorporate a statistical sampling plan. When a lot fails, the whole lot will have to be rejected - this may mean the lot has to be reweighed, repacked and labelled or whatever it takes to ensure that the lot will pass the rules.

Note: The examples shown relate only to the tests the Ministry will carry out. They are not sampling plans for industry to follow.

Responsibilities of packers, importers and retailers

Your main responsibility is to ensure that you comply with the Weights and Measures Act and Regulations. To do this you should ensure that the packages pass a special statistical test called a 'reference test'. This is conducted by a MAPSS Officer and shows whether the packer complies with the three AQS rules. Packers, importers and retailers should consider checking the quantity of packages through statistical sampling techniques, as part of a quality management system.

Checking systems and sampling

If you decide to check your packages using a statistical sampling plan, we recommend that you seek advice on what is best for your business. You may find advice from

• in house expertise
• contacting a quality consultant or statistician
• reference books on statistics and sampling
• overseas codes of practice on sampling 1
• international standards on sampling 2
• information on the web.

1. UK DTI Code of Guidance for Packers and Importers. Available from UK HMSO via bookshops or online.
2. ISO 2854 on Statistical Interpretation of data.
3. ISO 2859 Sampling procedures.

Weighing and measuring equipment

Equipment used for check weighing packaged goods must be suitable for the purpose for which it is being used. You can ask the Measurement and Product Safety Service (MAPSS) for advice on this. The Ministry recommends annual calibration of all weighing and measuring equipment as part of your quality management system. Testing, verification and certification may be carried out by accredited persons. Details of accredited persons are available from the MAPSS.

How reference tests work

Reference tests for weight or measure

In the Examples table shown below, 3500 packs of butter are identified as the lot. Using Table 1, 32 packs of butter are chosen at random as the sample. Table 2 shows that a 500g net package is allowed a T of 3% or 15g. Therefore a non-standard package is allowed to contain between 485g and 470g.

A package with a weight of less than 470g would be an inadequate package. The reference test identifies two non-standard and no inadequate packages, and that the average net weight is equal to 501g. The packages of butter pass all three rules.

If potatoes had been chosen from the Examples table, an inspection lot of 148 would have resulted in a sample size of 12 packages. Table 2 indicates a T of 1.5% (45g) for a 3kg bag. The reference test identifies no non-standard and one inadequate package. The lot fails the reference test because it identifies one inadequate package when none are permitted. (Rule 3).

Examples table

Examples of Ministry reference tests for weight (mass) or measure (volume)

Reference tests for number

Consider packages of oysters labelled '12 Pacific Oysters'. There are a total of 50 packs which make up the lot. Therefore, using Table 1, 12 packs must be chosen at random to form the sample.

A reference test identifies that 10 out of 12 packs contain a dozen oysters, one pack contains 13 oysters, and the other 11 oysters. This means the lot passes, as by reference to Table 3, one item is the deficiency allowed for packages containing 50 or less items.

For the second example mild steel washers are chosen. Each of the 500 packs contains 200 washers, according to their labels. Therefore the sample size is 32 packs chosen at random. A reference test identifies five packs that contain 195 washers. The tolerable deficiency for packs containing more than 50 items is 2% rounded up to the nearest whole number - in this example that would be four washers - and the number of non-standard packs permitted would be four. Therefore the lot fails the reference test.

Statistical sampling and tolerancies tables

Table 1 Inspection lots and sampling characteristics

Table 2 Tolerable deficiencies for packages labelled by mass or volume

Table 3 Tolerable deficiencies for packages labelled by length, width, area or number

NOTE: The figures in these tables are taken from the regulations (Schedule 7A - Weights and Measures Regulations 1999) and the Ministry will use these when carrying out AQS checks on your packaged goods.

Ministry visits

MAPSS Officers will periodically visit packers and importers to routinely check packages. They will try to keep disruption to a minimum. Checks on packages at source are more effective than those carried out at retail level and it allows officers to monitor products more easily. MAPSS officers will also continue to carry out inspections at retail outlets.

MAPSS Officers can be contacted at any of the MAPSS Offices for advice on the regulations. If you need assistance in complying with the new system, the MAPSS Officers can arrange to visit you.

Glossary

Lot (of packages): A collection of packages containing goods that are

1. of the same kind
2. of the same stated weight, measure, or number
3. available for inspection at the same time and place.

The size of a lot will be determined by the MAPSS Officer at the time of checking. As an example, a lot may be an hour's production run or it may be a stacked quantity of packages not exceeding 10,000.

Packaged goods: Any goods intended for sale that are contained or wrapped in a package of any sort, and whose stated net quantity has been decided upon before packing.

Packer: A person who weighs, measures or counts goods into packages. However this may not necessarily be the person named on the package, or the person whose brand or trademark appears on the label.

Random sample: A specified number of packages taken from a lot, in such a way that each package has the same probability of being chosen.

Tolerable deficiency (T): The amount of error that is allowed for packages as set out in Schedule 7A Tables 2 & 3 of the Weights and Measures Regulations 1999.

Desiccating goods: Any packaged goods that lose weight or volume through evaporation when the package is made up. The Ministry of Consumer Affairs will consider whether products are desiccating on a case by case basis. Desiccating goods must fulfil the three rules if they are tested during a seven-day period starting after the day they were packed. After this no package may be an inadequate package.

Catchweight goods: Packaged goods that are usually sold in varying quantities eg joints of meat. AQS checks will not apply, but selling shortweight is still an offence.

Reference test: The test our officer will carry out on your packaged goods.

Note:

This information is intended as a guide to the Average Quantity System. It is not an authoritative guide to the legal requirements of selling by quantity and should not be substituted for the Weights and Measures Act 1987 (as amended by the Weights and Measures Amendment Act 2000 - 2000 No 86) and Weights and Measures Regulations 1999 (Weights and Measures Amendment Regulations 2001 - 2001/305)

We recommend that you consider purchasing a copy of the amended Act and Regulations. Copies can be ordered from bookshops.