Weighing and Scales FAQs

Yes. There are numerous OIML Recommendations that cover the wide range of content in the scale-relevant sections of NIST Handbook 44. 

Please see a complete crosswalk between NIST Handbook 44 and OIML Recommendations here.

When selecting a scale for a particular application, several aspects need to be considered:

• Suitability.  Most importantly, the scale must be suitable for the product that is being weighed. For example, a scale for weighing fertilizer should be corrosion resistant.
• Accuracy. The accuracy class of the scale must be appropriate for the application. The typical accuracy classification for various weighing applications are provided in Table 7a “Typical Class or Type of Device for Weighing Applications” of NIST Handbook 44, section 2.20, requirement UR.1.1.
• Capacity. The maximum load that can be expected to be weighed should not exceed the capacity of the scale.
• Minimum Load. The minimum load that can be expected should exceed the amounts noted in Table 8 “Recommended Minimum Load” of NIST Handbook 44, section 2.20, requirement UR.3.1. As a result, this minimum load defines the required verification scale interval, e.  For example, if a class III scale will be used to weigh loads of 0.25 lb or more, the e should be no greater than 0.01 lb.  If the load on a class II scale will be no less than 100 g, then the value of e should be no greater than 2 g.
• Usability considerations. Any other desired functionality for the scale’s usability, such as price calculation, network capability, etc., will need to be considered on a case-by case basis.

Scales used for commercial applications must comply with the laws of the state in which it will be used as a legal metrology device. Since all 50 US states have adopted NIST Handbook 44, the most important aspect is that the scale has an active NTEP Certificate of Conformance as proof that it is compliant with NIST Handbook 44. Note that NIST OWM does not recommend or endorse any particular scale types.

Before a scale can be used for commercial applications, it must be inspected and approved by an authorized body of the state it is used in. Click here for a listing of state and territory weights and measures offices and contact information.

Commercial applications are defined in NIST Handbook 44, section 1.10 General Code, G-A.1 as applications in which a weighing instrument is being used or employed:

1. in establishing the size, quantity, extent, area, composition (limited to meat and poultry), constituent values (limited to grain), or measurement of quantities, things, produce, or articles for distribution or consumption, purchased, offered, or submitted for sale, hire, or award;
   
   For example, a scale at the deli in the grocery store.
    
2. when assessing a fee for the use of the equipment to determine a weight or measure;
   
   For example, a vehicle scale at a truck stop allows drivers to check the weight of their trucks.
    
3. in determining the basis of an award using count, weight, or measure; or
   
   For example, the scale used at a fishing contest.
    
4. in computing any basic charge or payment for services rendered on the basis of weight or measure.
   
   For example, a postal scale or the luggage scale at the airport.

The scale division, d, is the actual resolution of a scale (analog or digital). The verification scale division, e, is a measure of the accuracy of the scale and is used to define the scale classification and to determine the tolerances. Every scale (that falls under the Scale Code, section 2.20 of NIST Handbook 44) has a verification scale division, e. But not every scale has an indication (e.g., a balance), and therefore, not every scale has a scale division, d.

As the verification scale division, e, relates to the accuracy of the scale, all tolerances defined in the Scale Code, section 2.20 of NIST Handbook 44, are expressed in e. Some requirements relate to the scale division, d, but those requirements do not define any tolerances.

For scales of accuracy classes III, IIIL, and IIII, (used in most applications), the scale division, d, must be equal to the verification scale division, e (i.e., the resolution of the indication must be approximately the same as the accuracy of the scale). Only scales of class I and II may have a scale division, d, smaller than the verification scale division, e. But that does not mean that the scale is more accurate. To avoid a false sense of accuracy, the digit indicating the smaller scale division, d, must be clearly differentiated from the other digits.

Note:  Item SCL-23.3 on the 2023 NCWM S&T agenda aims to correct inconsistencies regarding the use of the terms “scale division” and “verification scale division” in NIST Handbook 44.

Click here for additional information.