NIST OWM Technical Article

Min Marking-Class I & Class II Scales Page 1 of 7 Rev-4-15-20

Making Sense of the “Min” marking on Class I and Class II Scales

Rick Harshman NIST OWM Legal Metrology Devices Program

If you’ve been involved lately in the inspection of high-precision Class I and/or Class 

II scales, you’ve probably noticed some scale manufacturers are designating a 

“Min” value by marking it on the scale. This marking generally appears on the 

reading face of the scale. Like me, you’ve probably thought of the “Min” value as 

being the minimum acceptable load to be weighed for the scale to be suitable for 

its application based on its accuracy class. After all, who best to specify a minimum

acceptable load than a scale’s manufacturer? If, however, you delved a little

deeper and considered this value in relation to the value of the verification scale 

division (e) and scale division (d) on scales you’ve inspected, you will have noticed 

the “Min” value can sometimes be as small as 5 (e) on scales in which (e) and (d) 

are different values. 

The marking of such a small “Min” value in relation to a scale’s verification scale 

division raises a lot of questions, especially considering such designation is that of

the manufacturer. Some of the common questions that have been raised by 

inspectors and industry include:

• What is “Min” and why are some scale manufacturers marking its value on 

scales they produce?

• Why, in some cases, is the value designated so small (e.g., only 5 (e)?

• Can a scale be considered suitable for weighing loads this small?

• How does the “Min” value specified on a scale relate to the recommended 

minimum loads specified in NIST Handbook 44 (HB 44) Scales Code Table 8?

The purpose of this article is to answer these questions and provide guidance to 

field officials on determining the smallest acceptable load to be weighed on scales 

they are inspecting. First let's review some terminology associated with the values 

and increments displayed on a scale used in NIST Handbook 44. Those terms and 

their definitions are as follows: 

scale division, value of (d). – The value of the scale division, expressed in 

units of mass, is the smallest subdivision of the scale for analog indication or 

the difference between two consecutively indicated or printed values for 

digital indication or printing. (Also see “verification scale division.”) [2.20, 

2.22]
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Min Marking-Class I & Class II Scales Page 2 of 7 Rev-4-15-20

verification scale division, value of (e). – A value, expressed in units of 

weight (mass) and specified by the manufacturer of a device, by which the 

tolerance values and the accuracy class applicable to the device are 

determined. The verification scale division is applied to all scales, in 

particular to ungraduated devices since they have no graduations. The 

verification scale division (e) may be different from the displayed scale 

division (d) for certain other devices used for weight classifying or weighing 

in pre-determined amounts, and certain other Class I and II scales. [2.20]

Note from the definition of “verification scale division, value of (e)” that the value 

of (e) is specified by the manufacturer of the device. The value of (e) is not required 

to be marked on a scale if it equals the value of (d) and on most scales, such a 

designation is not present since (e) and (d) are typically equal. 

“Min” is an abbreviation used in International Recommendation OIML R 76 Nonautomatic weighing instruments(R 76) for the term “Minimum Capacity.” The term 

is defined in R 76 as follows:

Minimum capacity (Min) Value of the load below which the weighing results 

may be subject to an excessive relative error. 

R 76 also specifies that the value of the minimum capacity (Min) is designated to 

indicate that use of the instrument below this value is likely to give rise to 

considerable relative errors. 

The criteria contained in R 76 is intended for type evaluation and not field 

enforcement. For this reason, there are no user requirements included in R 76. 

The marking of a scale’s minimum capacity (Min) is a requirement of R 76. Its 

designation on a scale submitted by a manufacturer to OIML for certification makes

possible the issuance of an OIML Certificate once all other type-evaluation criteria 

is met. The issuance of an OIML Certificate provides opportunity for a 

manufacturer to market scales internationally in the different countries that adopt 

OIML R 76 and require an OIML Certificate.

NIST Handbook 44 (HB 44, which has been adopted in some form by all U.S. weights 

and measures jurisdictions) does not require a “Min” value be marked on scales; 

but instead, includes a User Requirement in the Scales Code that provides 

recommended minimum loads based on a scale’s accuracy class. OWM views the 

meaning of the OIML term, “Minimum capacity (Min)”and the HB 44 term, 
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Min Marking-Class I & Class II Scales Page 3 of 7 Rev-4-15-20

“minimum load” to be the same. Although not required by HB 44, it is likely the 

“Min” marking appears on many of the commercial application scales sold in the 

U.S. because it is more cost effective for manufacturers to build a single scale with 

a common marking for both international and U.S. markets. 

The parameters for scale accuracy class included in R 76 Table 3 Classification of 

Instruments (recreated below) are nearly identical to those in HB 44 Scales Code 

Table 3 Parameters for Accuracy Class. One significant difference is that R 76 does 

not recognize the HB 44 Class IIIL as an accuracy class, which is why it is not included 

in the table below. Some less significant differences are:

• R 76 limits the maximum number of scale divisions for Class IIII scales to 

1 000, whereas HB 44 specifies a maximum of 1 200 divisions. 

• There is an exception in R 76 Table 3 for Class I scales. The exception, found 

in R 76 paragraph 3.4.4.,states that the minimum of 50 000 verification scale 

intervals does not apply to Class I scales with d ˂ 0.1 mg. No such exception 

exists in HB 44.

Accuracy

class

Verification

scale interval, e

Number of verification

scale intervals,

n = Max/e

Minimum

capacity,

Min

(Lower limit)

minimum maximum

Special

(I)

0.001 g ≤ e* 50 000** – 100 e

High

(II)

0.001 g ≤ e ≤ 0.05 g

0.1 g ≤ e

100

5 000

100 000

100 000

20 e

50 e

Medium

(III)

0.l g ≤ e ≤ 2 g

5 g ≤ e

100

500

10 000

10 000

20 e

20 e

Ordinary

(IIII)

5 g ≤ e 100 1 000 10 e

* It is not normally feasible to test and verify an instrument to e < 1 mg, due to the uncertainty of the 

test loads. 

** See exception in 3.4.4.

OIML R 76 Table 3 (Classification of Instruments)

Notice too, Table 3 of R 76 includes an additional column to the right, which 

provides the Minimum capacity (Min) for the different accuracy classes of scales. 

The values specified in this column correspond to the “recommended” minimum 

loads specified in HB 44 Scales Code Table 8. What makes the “Minimum capacity 

(Min) values” specified in R 76 Table 3 different than the “recommended minimum 
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Min Marking-Class I & Class II Scales Page 4 of 7 Rev-4-15-20

load values” specified in HB 44 Scales Code Table 8 are instructions contained in 

OIML R 76 paragraph 3.4.3. Minimum capacity. These instructions in R 76 are to 

replace the verification scale interval (e) with the actual scale division (d) in the last 

column of Table 3 (i.e., the last column to the right). R 76 paragraph 3.4.3. is copied 

below. 

3.4.3 Minimum capacity 

The minimum capacity of the instrument is determined in conformity with the requirements in Table 3. 

However, in the last column of this Table, the verification scale interval, e, is replaced by the actual scale 

interval, d.

OIML R 76 Paragraph 3.4.3 Minimum capacity

OWM’s understanding of these instructions (in paragraph 3.4.3) is that when (e) 

and (d) are different values on a scale (which is often the case with Class I and II 

scales), it is the (d) value on which scale manufacturers are to base the marking of 

“Min.” Several photos of Class I and Class II scales recently shared with OWM by 

different states provide an indication that scale manufacturers are, in fact, basing 

the Min marking on the value of (d), rather than (e). That is, on photos of scales in 

which a “Min” value is marked, its value equals the product of multiplying the Mincapacity value corresponding to the scale specified in Table 3 by the scale’s value 

of (d). That is:

(Min-capacity value in Table 3) x (scale’s value of “d”)

This equation accounts for why the marked Min value can be as little as 5 (e) on 

some scales. That is, when the value of (d) is one-tenth (e) and the Min-capacity 

value in Table 3 is 50 (which corresponds when the value of e ≥ 0.1 g on Class II 

scales), multiplying the factor “50” by the value of (d) results in a product equal to 

only 5 (e). 

Example: Class II scale: e = 0.1 g d = 0.01g

50 x 0.01 g = 0.5 g

Such marking, unfortunately, conflicts with OWM’s interpretation (and seemingly 

that of many U.S. weighing experts) of how the values in HB 44 Scales Code Table 

8 apply to scales in which (e) and (d) are different values. That is, the opinion that 

recommended minimum loads are to be based on the value of (e), not (d), since 

both “parameters for scale accuracy class” and “applicable tolerance values” in HB 
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44 are based on the verification scale division (e). OWM notes it was recently 

concluded by the National Type Evaluation Program’s (NTEP’s) administrator; the 

NTEP Weighing Sector’s technical advisor; and NTEP weighing evaluators (during 

the 2018 NTEP Lab Meeting); and members of the Weighing Sector (during the

2019 Weighing Sector Meeting), that the application of NIST HB 44 requirements 

in all cases are intended to be based on the verification scale division (e). This 

would include the recommended minimum load values specified in Scales Code 

Table 8. This conclusion aligns with a guiding principle of HB 44 that the same 

requirements should apply to scales used in the same application regardless of 

technology or design. 

It is important to base a scale’s minimum acceptable load on the value of (e) when 

considering the effects of tolerance application and digital rounding. The HB 44 

maintenance tolerance applicable to Class I and Class II scales is as follows:

Accuracy Class Test Loads

(e)

Maintenance 

Tolerance

(HB 44)

Class I 0 to 50 000 e 1 e

Class II 0 to 5 000 e 1e

This tolerance of 1 (e), alone, can result in a considerably large relative error when 

basing the minimum acceptable load on the verification scale division (e). For 

example, the recommended minimum load specified in Scales Code Table 8 for a 

Class II scale having a value of (e) equal to 0.001 g to 0.05 g is 20 (e). If this scale

were used to weigh a load of 20 (e), the scale error of 1 (e) represents 5 % of the 

load weighed:

1 e ÷ 20 e = 0.05 x 100 = 5 %

Next, consider the effect of using the same scale to weigh a load equal to 20 (d). If

(d) were equal to one-tenth the value of (e) [which is normally the case for Class I 

and II scales with different values of (d) and (e)] an error of 1 (e) represents 50 % 

of a load of 20 (d):

1 e ÷ 2 e = 0.5 x 100 = 50 %
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Min Marking-Class I & Class II Scales Page 6 of 7 Rev-4-15-20

Note, the denominator of 2 (e) in these calculations is the equivalent of 20 (d) since

(d) = 1/10 (e) in this example.

This tenfold increase in relative error (i.e., from 5 % to 50 %) is solely the result of 

basing the minimum acceptable load on the (d) value, which in the example 

provided, is one-tenth the (e) value. These two examples highlight the importance 

of basing the minimum acceptable load on (e) when (e) and (d) are different values 

on a Class I or Class II scale. 

The potential error caused by the rounding of digital values to the nearest 

minimum increment is less of a concern on Class I and II scales when (e) and (d) are 

different values than when they are equal, providing both (e) and (d) are read 

together when using the scale. This is because when (e) and (d) are different values 

on a Class I or II scale, the value of (e) does not round, but rather advances and 

declines in value only at the point when the entire range of the (d) resolution has 

been exceeded. Because applicable tolerances are based on (e), any rounding 

effect of the (d) resolution can be considered negligible when (d) is one-tenth the 

value of (e); which is generally, but not always the case. 

It is because of the effect of tolerance application; digital rounding; and other 

factors which cause measurement uncertainty, that it is generally recommended 

most loads weighed on a scale be between one-quarter and three-quarters of scale 

capacity. Weighing of loads close to or equal in value to the recommended 

minimums specified in HB 44 Table 8 should not be the norm, but rather the 

occasional exception. OWM recognizes this is not always the case.

OWM is not aware of the reason(s) why a provision exists in R 76 specifying use of 

the actual scale division (d) to establish the minimum capacity to be marked on 

scales. Such marking on Class I and II scales with different values of (e) and (d) puts 

U.S. field officials in a very challenging position if they strive to properly enforce 

scale suitability by using the (e) value to determine minimum acceptable loads. 

R 76 is currently under revision, having last been revised in 2006. Because there is 

disagreement between R 76 and HB 44 with respect to the determination of the

minimum acceptable load, OWM recently drafted an e-mail inquiry to the 

Conveners of R 76 (Germany and France) requesting an explanation of the 

technical justification for using (d) rather than (e) for this determination on Class I 

and II scales. There has been no response to date on this inquiry. Additionally, 

OWM discussed the concern with NTEP’s Administrator, who concurred the 
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recommended minimum loads specified in Table 8 are intended to be based on the 

(e) value in all cases. OWM requested NTEP consider adding a statement to the 

NTEP Certificates of Conformance for those Class I and II scales in which (e) and (d)

are different values, making clear the “Min” marking represents the minimum 

capacity value, which is an OIML marking requirement. In the U.S., recommended 

minimum loads are based on a scale’s verification scale division (e). OWM’s 

request is currently being considered by NTEP.

During the 2020 NCWM Interim Meeting, the Specifications and Tolerances

Committee agreed to request the Chairman of the NCWM form a Task Group to 

review the Scales Code of NIST Handbook 44 and relevant portions of OIML R 76

and recommend changes as necessary to:

1. Clarify how error is determined in relation to the verification scale division 

(e) and the scale division (d);

2. Clarify which is the proper reference throughout the Scales Code:

a. the verification scale division (e); or

b. the scale division (d) 

3. Ensure proper selection of a scale in reference to the verification scale 

division (e) and the scale division (d); and

4. Clarify the relationship between the verification scale division (e) and the 

scale division (d)

Assuming the Chairman agrees to this request, OWM expects the Min capacity

issue along with other concerns related to the use of (d) and (e) to be further 

discussed and addressed by the NCWM Task Group.

For additional information relating to this article, contact Rick Harshman by email 

atrichard.harshman@nist.gov or by phone at (301) 975-8107.