What is Legal-For-Trade?
Legal-for-trade status is required when a scale or measuring device is used in commerce. But what does that status mean, exactly? To obtain a legal-for-trade classification, a measurement equipment manufacturer must submit their device for evaluation through NTEP, a program administered by the National Conference on Weights and Measures (NCWM). Through this program, rigorous testing is performed to determine if the device meets strict requirements, including specifications regarding operating procedures, readability, how it is affected by temperature & more. If the scale or weighing device passes the evaluation, the manufacturer is awarded a Certificate of Conformance number, which they can use to market and sell their product as a “legal-for-trade” device.
This classification lets buyers know that the device can legally be used in commerce. However, it’s not just a “plug-and-play” device after that. Let’s examine the legal-for-trade evaluation process, the classes of legal-for-trade equipment, and the process of getting an approved device up & running.
How is Legal-For-Trade Testing Performed?
The National Type Evaluation Program, or NTEP, is the evaluation program that determines whether a device is “legal-for-trade”. This is why legal-for-trade scales are sometimes referred to as “NTEP approved”. The program is administered by the National Conference on Weights and Measures (NCWM) in the United States. NTEP testing is meant to determine whether the device meets the criteria outlined in Handbook 44. Handbook 44 is published by NIST and provides the weighing & measurement industry with standard procedures for verifying weighing & measurement device accuracy. It is the nationally accepted standard on Specifications, Tolerances and Other Technical Requirements for Weighing and Measuring Devices.
The NTEP Evaluation Process
The NIST website describes the NTEP program here. Basically, NTEP, or the National Type Evaluation Program, requires that any device used in commerce (or marked legal-for-trade) undergo an approval process. The process involves sending the weighing device to a lab, where it is put through rigorous test procedures to ensure that it meets the “uncertainties which are related to tolerances associated with the intended final use in the marketplace.” (Source: NIST)
These steps must be completed for every device that a manufacturer wishes to have classified as “legal-for-trade”:
- The applicant (typically the device manufacturer) completes & submits the NTEP application & payment to the NCWM.
- A lab will perform test procedures on the device in question to ensure that it meets the requirements to be considered “legal-for-trade”. The lab will work directly with the party who submitted the application.
- If the device is approved, a Certificate of Conformance will be activated & posted to the NTEP Certificate of Conformance database.
- The applicant must pay annual NTEP maintenance fees to keep the device’s Certificate of Conformance active.
Accuracy Classes for Legal-For-Trade Scales
Once a scale or weighing device has been approved by NTEP to be used in legal-for-trade applications, it is further classified into an accuracy class. The accuracy class in which a device is classified depends upon the number of scale divisions it can perform. Those parameters are outlined in the table below, obtained from Handbook 44.
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Table 3. Parameters for Accuracy Classes |
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Class |
Value of the Verification Scale Division (d or e1) | Number of Scale4 Divisions (n) | |
| Minimum | Maximum | ||
| SI Units | |||
| I | equal to or greater than 1 mg | 50 000 | –– |
| II | 1 to 50 mg, inclusive | 100 | 100 000 |
| equal to or greater than 100 mg | 5 000 | 100 000 | |
| III2,5 | 0.1 to 2 g, inclusive | 100 | 10 000 |
| equal to or greater than 5 g | 500 | 10 000 | |
| III L3 | equal to or greater than 2 kg | 2 000 | 10 000 |
| IIII | equal to or greater than 5 g | 100 | 1 200 |
| U.S. Customary Units | |||
| III5 | 0.0002 lb to 0.005 lb, inclusive | 100 | 10 000 |
| 0.005 oz to 0.125 oz, inclusive | 100 | 10 000 | |
| equal to or greater than 0.01 lb | 500 | 10 000 | |
| equal to or greater than 0.25 oz | 500 | 10 000 | |
| III L3 | equal to or greater than 5 lb | 2 000 | 10 000 |
| IIII | greater than 0.01 lb | 100 | 1 200 |
| greater than 0.25 oz | 100 | 1 200 | |
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1 For Class I and II devices equipped with auxiliary reading means (i.e., a rider, a vernier, or a least significant decimal differentiated by size, shape, or color), the value of the verification scale division “e” is the value of the scale division immediately preceding the auxiliary means.
2 A Class III scale marked “For prescription weighing only” may have a verification scale division (e) not less than 0.01 g. (Added 1986) (Amended 2003)
3 The value of a scale division for crane and hopper (other than grain hopper) scales shall be not less than 0.2 kg (0.5 lb). The minimum number of scale divisions shall be not less than 1000.
4 On a multiple range or multi-interval scale, the number of divisions for each range independently shall not exceed the maximum specified for the accuracy class. The number of scale divisions, n, for each weighing range is determined by dividing the scale capacity for each range by the verification scale division, e, for each range. On a scale system with multiple load-receiving elements and multiple indications, each element considered shall not independently exceed the maximum specified for the accuracy class. If the system has a summing indicator, the nmax for the summed indication shall not exceed the maximum specified for the accuracy class. (Added 1997)
5 The minimum number of scale divisions for a Class III Hopper Scale used for weighing grain shall be 2000.) |
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[Nonretroactive as of January 1, 1986]
(Amended 1986, 1987, 1997, 1998, 1999, 2003, and 2004)
Source: NIST Handbook 44
Getting an NTEP Approved Scale Placed In Service
Once a company purchases an NTEP approved, or “Legal-For-Trade” scale, can the operator plug it in and use it in commerce? No. Before a scale or measurement device can used in commerce, it must be inspected & certified by a state inspector and/or “placed in service” by a state-licensed service provider like the Michelli Weighing & Measurement team. (Even if it is a legal-for-trade device.) When the Michelli Weighing & Measurement team places a device in service, we coordinate with the state inspector to ensure that the process is seamless for our customer.
The Registered Service Agent, or RSA, must submit a “Placed In Service Report”, or PIS report. PIS reports contain details of the Registered Service Agency, location of the device, and device information, including but not limited to its manufacturer, model number, serial number, NTEP Certificate of Conformance number, and capacity. The service agent must sign the document to certify that the device was installed according to NIST Handbook 44 procedures, and submit that report to the state or local governing body. Once this process is complete, the state or local governing body will place its seal on the scale or measuring device, and it is ready to be used in legal-for-trade applications.
Maintaining A Legal-for-Trade Device
The process to have a scale or measuring device classified as “NTEP approved” or “legal-for-trade” is quite rigorous. This is meant to ensure that device(s) used to measure the material(s) being sold has been manufactured to specifications that should enable it to produce accurate measurements. However, equipment needs to be properly maintained in order to continue to perform properly. No matter how well a scale or device was manufactured, if it is bumped, overloaded, dirty, or otherwise “roughed up”, it could fall out of tolerance and produce inaccurate readings. Alternatively, the centrifugal force of the earth, elevation of the area in which the scale is located, and a slough of other factors could also impact the device’s ability to produce accurate readings. This is why it’s so important to have scales & measurement equipment serviced & calibrated regularly. The importance of an accurate reading will dictate how often the equipment should be calibrated. So, if the material being sold is highly valuable, even a few pounds left off could cost the business or consumer a significant amount of money. In that instance, the scale should be calibrated more frequently than one that weighs more inexpensive materials.
The Michelli Weighing & Measurement team is here to help. Our Account Managers are product specialists and can help you determine which NTEP approved equipment is right for you based on your application, environment & budget. The Michelli Weighing & Measurement team is a registered service agent in 11 states, meaning we can place your legal-for-trade device into service. Beyond that, our expert service technicians are factory-trained in maintenance and repair of scales, lab balances & a wide range of measurement equipment. We also have ISO 17025 accredited calibration labs throughout the Southern & Western United States, with metrologists at the ready to maintain, repair & calibrate your precision measurement equipment. Michelli Weighing & Measurement is your partner for weighing & measurement equipment purchase, rental and service.
Need Help Choosing a Legal-for-Trade Scale?
Contact your nearest Michelli Weighing & Measurement location today to speak with our experts. We can help you find the best legal-for-trade equipment and get it placed in service.