Net Contents Control
What is Net Contents Control?
Net Contents Control is a method that ensures consumers get what they pay for. When consumers purchase a product, they expect and deserve to receive at least as much product as the amount stated on the product label.
Federal law (in the U.S. and other countries) protects consumers from intentional or unintentional “shorting” of the contents of any product they purchase. Government regulations impose stiff penalties on manufacturers that fail to meet their label claims. Additionally, manufacturers’ reputations suffer if they are perceived to short-change their customers.
In this environment, many business leaders take a cautious approach. They protect their reputations by putting systems in place that guarantee compliance and then accept some level of product give-away as the cost of doing business.
Fortunately, there are well-established, time-tested methods that enable manufacturers to scientifically optimize their processes to both ensure compliance AND minimize product give-away.
How are net contents regulated?
The U.S. Department of Commerce (through the National Institute of Standards and Technology) publishes the definitive guide for Net Content Control of packaged goods sold in the United States: NIST Handbook 133, “Checking the Net Contents of Packaged Goods”. (Last accessed 17 October 2018)
The Handbook requires that the net quantity of contents statement must be accurate, but allows for reasonable variations. The guiding paragraph states:
The net quantity of content statement must be “accurate,” but reasonable variations are permitted. Variations in package contents may be a result of deviations in filling. The limits for acceptable variation are based on current good manufacturing practices in the weighing, measuring, and packaging process. The first requirement is that accuracy is applied to the average net contents of the packages in the lot. The second requirement is applied to negative errors in individual packages. These requirements apply simultaneously to the inspection of all lots of packages except as specified in Section 1.2.5 “Exceptions to the Average and Individual Package Requirements.
Guidelines for Acceptable Variation
The Handbook recognizes that some variation in filling processes is inevitable, and provides guidelines for acceptable variation. These guidelines take the form of two requirements for compliance:
- In an inspection lot, the average of all of the packages must be at least equal to the label claim on the package.
- No individual package may be under filled by more than the Maximum Allowable Variation (MAV).
These requirements may be visualized as follows:
The Mean (M) must be above Label Claim (Label), and no individual value (represented by the Green band) may be below the MAV. Note that the x-axis is the weight or volume of individual packages, and the y-axis represents the counts of packages in each size.
Competing Needs of the Consumer and the Producer
The NIST 133 regulation places competing demands on the producer. On the one hand, the producer must make sure the consumer gets what they pay for. On the other hand, anything extra they put in the package reduces their profits. This is known as overfill or overpack.
The Handbook turns over the problem of overfill to the manufacturer: “This handbook does not specify limits of overfilling, which is usually controlled by the packer.”
The packer meets federal regulation if they make sure the Mean of any inspection lot is above the Label Claim. If they put more in the package, neither the consumer nor the regulators will complain.
Anything to the right of the Label Claim (the yellow band above the Mean line) is overfill. Overfill represents profits that are given away to customers. While packers cannot completely avoid overfill, the closer the Mean to the Label Claim, the less overfill.
Why are check weigh systems insufficient?
Many packers build Net Content Control around sophisticated, state-of-the-art check weigh systems. These systems ensure compliance, but do nothing to minimize overfill.
Most check weigh systems rely on some kind of specification, usually MAV and Label Weight. The systems reject individual units when they weigh below some preset target. Typically, these systems do not look at trends or provide knowledge to continuous improvement teams that can lead to optimized fill weights. Rather than giving packers actionable knowledge, they encourage users to “play it safe.” This can leave significant amounts of money in the package.
The good news is that by making better use of real-time, actionable information, packers can have it both ways. They can “play it safe” and at the same time optimize their material resources.
Why GainSeeker Suite SPC Software for Net Contents Control?
GainSeeker Suite is the real-time manufacturing intelligence platform. Built on robust Statistical Process Control tools, GainSeeker:
- Integrates with digital scales and inline check weigh systems to automate data capture.
- Alarms operators and inspectors with real-time alerts when the process shifts.
- Extends alarms to engineers and other stakeholders so problems can be addressed quickly.
- Provides user-configurable, role-based dashboards to ensure all stakeholders are in the know.
- Analytic wizards remove time-consuming guesswork by automatically pinpointing sources of variation.
- Is supported by the GainSeeker Platform Library, with a complete Overfill and Package Weight Control Kit available for download and installation. The Overfill and Package Weight Control Kit speeds implementation.
- Includes the Overfill Wizard (AKA Overpack Wizard). The Overfill Wizard makes it easy to calculate the expected return on investment in reducing Overfill. You can read about the Overfill Wizard in GainSeeker Help.
Case Study: Estimating Product Giveaway
A food manufacturer provided Hertzler Systems with scanned copies of On-line Test Sheets. These sheets provide approximately 15 hours of weight data taken from one product, on one fill line.
Header information from these pages identified the product, target weight, label claim, MAV, and so forth. The relevant columns include the Tester Initials (column 1), Time (2 & 3), Weights (4 & 5), and comments (14). In addition, the food manufacturer personnel also provided estimates or actual values for material costs and production volumes.
Hertzler Systems staff entered this data into a proprietary weight control calculator. The calculator returns several critical values: Mean, Percent Overfill, Cost of Overfill, and the number of MAV Violations. With this information in hand, we can manipulate “what if?” variables to design an optimized system. This enables us to compare the current cost of Overfill with a projected Overfill cost under various scenarios.
Inputs and Assumptions
We assumed that each line is capable of producing 70,000 packages a day and that the process is running 24 hours a day, 7 days a week, producing approximately 6.3 Million units per month. The price per gram is $0.00413 ($4133/1000KG). In a production environment, this information might come from direct integration to another business system.
|Weight Control Calculator|
|Price per Unit||$ 0.00413|
|Packages per month||6,300,000|
|Improvement Target (Reduce Variation by)||25%|
|Shift target toward label weight||-2.3|
Based on an analysis of 140 weight measurements, the average for the lot was 666.25 G, and 80% of the lot was above Label Claim. The total Overfill, then, is $84,493.
We hypothesized a process improvement (Step 1) of 25%. This improvement did not cause a reduction in Overfill because approximately the same amount of material was given away.
Once we reduced the variation, we experimented with shifting the target (Step 2) towards the Label Claim. Our goal was to comply with the two foundational goals of NIST Handbook 133:
- The mean for the lot must be above Label Claim
- No individual may be below MAV
Through trial and error, we were able to determine that a 2.3 G shift in the target would ensure that 55% of the lot would be above Label Claim. (The mean would be 663.93G against a Label Claim of 663.0 G.) In addition, none of the individual values would be below MAV.
Step 2: Reduced Variation &
|Monthly Giveaway in $||$ 84,493||$ 24,606|
|% above Label Wt.||80%||55%|
|% below Label Wt.||20%||45%|
|Number of Mavs||0||0|
This Step 2 shift reduced Overfill to $24,606, a savings of nearly $60,000 per month, or nearly three-quarters of a million per year.
Graphically this shift can be shown as the move from Current situation:
|Monthly Giveaway in $||$ 84,493|
To Step 2: Shift Target:
|Monthly Giveaway in when variation is reduced and process shifted||$ 24,606|
|Total savings||$ 59,887|