Preliminary results of Euramet Rockwell comparison between INRiM and UME (EURAMET.M.H-S1.a.b.c)


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ACTA IMEKO 
ISSN: 2221-870X 
December 2020, Volume 9, Number 5, 256 - 260 

 
 

PRELIMINARY RESULTS OF EURAMET ROCKWELL COMPARISON  

BETWEEN INRiM AND UME (EURAMET.M.H-S1.A.B.C) 
 

C. Kuzu1, A. Germak2, C. Origlia3, E. Pelit4 

 
1 UME, Kocaeli, Turkey, cihan.kuzu@tubitak.gov.tr 

2 INRiM, Torino, Italy, a.germak@inrim.it  
3 INRiM, Torino, Italy, c.origlia@inrim.it 

4 UME, Kocaeli, Turkey, ercan.pelit@tubitak.gov.tr  

 

Abstract: 

A bilateral supplementary comparison between 

INRiM (National Metrology Institute of Italy) and 

UME (National Metrology Institute of Turkey) had 

been decided to be organized in the field of 

Hardness Metrology to determine the consistency of 

the national hardness standards in both countries 

realizing Rockwell Hardness measurements in 

accordance with ISO 6508-1:2016 [1] and ISO 

6508-3:2015 [2] standards. In this paper the 

procedure and preliminary measurement results of 

the bilateral EURAMET supplementary 

comparison between the two laboratories are 

explained.  

Keywords: Hardness, Rockwell, comparison, 

supplementary  

1. INTRODUCTION 

A bilateral supplementary comparison between 

INRiM (Istituto Nazionale di Ricerca Metrologica) 

and UME (TÜBİTAK Ulusal Metroloji Enstitüsü) 

was carried out in the field of Hardness Metrology 

to determine the consistency of the national 

hardness standards used in both countries realizing 

Rockwell Hardness measurements in accordance 

with the ISO 6508-1:2016 [1] and the ISO 6508-

3:2015 [2] standards, including the new definition 

of Rockwell Hardness scales accepted by the 

CIPM/CCM WGH [3]. The most important and the 

most widely used Rockwell Hardness scales such as 

HRA, HRBW and HRC constitute the scope of the 

comparison which was piloted by INRiM. 

The blocks used in the comparison as transfer 

standards were provided by UME. Each NMI 

measured five hardness levels for HRC and four 

hardness levels for HRA and HRBW scales on the 

same transfer standards, using both their own and 

common indenters which also were provided by 

UME by providing its own indenters. 

Measurements were carried out first by UME as the 

provider of the blocks, then by the pilot laboratory 

(PL) INRiM, then again by UME for checking the 

stability of the transfer standards.  

The NMIs were requested to realize the 

traceability of each component constituting the 

hardness scales on their national standards to the 

base SI units and constitute their uncertainty 

budgets before the comparison measurements. 

2. TRANSFER STANDARDS USED IN THE 
COMPARISON 

In the bilateral comparison a total of three sets of 

hardness reference blocks were used; one set for 

each hardness scale of HRA, HRBW and HRC, 

separately. Five blocks for HRC scale and four 

blocks for each of HRA and HRBW scales, a total 

of 13 hardness reference blocks were used. The 

blocks are placed in a wooden protective case 

during transportation with their anti-rusting paper 

and original cover provided by their producer. Some 

information related to the hardness reference blocks 

used in the comparison and their pictures are given 

below. 

Table 1: Hardness reference blocks for HRA scale 

No 
Hardness 

Value 

Serial 

Number 
Producer 

1 27 HRA 668-385 YAMAMOTO 

2 46 HRA 666-752 YAMAMOTO 

3 66 HRA 293-733 YAMAMOTO 

4 87 HRA 284-385 YAMAMOTO 

Table 2: Hardness reference blocks for HRBW scale 

No 
Hardness 

Value 

Serial 

Number 
Producer 

1 32 HRBW 668-326 YAMAMOTO 

2 53 HRBW 661-029 YAMAMOTO 

3 73 HRBW 666-251 YAMAMOTO 

4 95 HRBW 666-850 YAMAMOTO 

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mailto:cihan.kuzu@tubitak.gov.tr
mailto:a.germak@inrim.it
mailto:c.origlia@inrim.it
mailto:ercan.pelit@tubitak.gov.tr


ACTA IMEKO | www.imeko.org December 2020 | Volume 9 | Number 5 | 257 

Table 3: Hardness reference blocks for HRC scale 

No 
Hardness 

Value 

Serial 

Number 
Producer 

1 25 HRC 492-096 YAMAMOTO 

2 36 HRC 489-678 YAMAMOTO 

3 45 HRC 369-719 YAMAMOTO 

4 57 HRC 454-774 YAMAMOTO 

5 67 HRC 486-336 YAMAMOTO 

 

The pictures of the transfer standards used in the 

comparison with their nominal hardness values and 

serial numbers are given below. Their surfaces were 

cleaned with soft material before and after 

measurements when it is needed. 

   

  
S/N: 668-385, 27 HRA S/N: 666-752, 46 HRA 

  

S/N: 293-733, 66 HRA S/N: 284-385, 87 HRA 

Figure 1: Transfer Standards for HRA scale 

 

  

S/N: 668-326, 32 HRBW S/N: 661-029, 53 HRBW 

  

S/N: 666-251, 73 HRBW S/N: 666-850, 95 HRBW 

Figure 2: Transfer Standards for HRBW scale 

  
S/N: 492-096, 25 HRC S/N: 489-678, 36 HRC 

  

S/N: 369-719, 45 HRC S/N: 454-774, 57 HRC 

 

S/N: 486-336, 67 HRC 

Figure 3: Transfer Standards for HRC scale 
 

3. COMPARISON PROCEDURE 

It was requested that each participant shall assure 

that the national standards to be used in the 

comparison at least were in accordance with the ISO 

6508-1:2016 [1] and the ISO 6508-3:2015 [2] 

standards. Under these circumstances the 

components to be calibrated/verified are as follows; 

• Force (preliminary load, total load, preliminary 
load after removal of the additional load). 

• Testing cycle (in accordance with the new 
definition of HRC scale accepted by the CCM 

WGH [3] or at least in accordance with the ISO 

6508-1:2016 [1] and the ISO 6508-3:2015 [2] 

standards). 

• Indenter geometrical parameters (in accordance 
with the ISO 6508-3:2015 [2] standard). 

• Depth measurement system (in accordance with 
the ISO 6508-3:2015 [2] standard). 

Beside management of calibration of the 

components given above, the blocks were placed in 

the laboratory one day before the measurements for 

temperature equilibrium. The measurement steps 

realized during the comparison measurement are as 

follows; 

• Before starting the measurements, it was 
assured that the standardizing machines were 

working properly in accordance with their 

design parameters and the relevant ISO 

standards’ requirements. 

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ACTA IMEKO | www.imeko.org December 2020 | Volume 9 | Number 5 | 258 

• It was assured that the anvil where the blocks 
are seated on and both surfaces of the reference 

blocks were clean. 

• It was assured that the relevant scale and related 
indenter and other requirements were 

mounted/selected etc. 

• The ambient temperature was recorded. 

• Two sets of 7 measurements (with the two 
indenters, one common and one own) uniformly 

distributed on the surface of the block were 

made and recorded on the data form. 

• The ambient temperature was recorded. 

Seven measurements were carried out: the first two 

were discarded in order to eliminate the effects 

coming from adaptation of the machine and the 

blocks. In the calculations the last five indentations 

were taken into consideration. The first two 

indentations were recorded but not used in the 

calculations. 

4. REFERENCE VALUES OF INFLUENCE 
PARAMETERS 

In the calibration of hardness reference blocks 

the calibration laboratories realize this work in 

accordance with some internationally defined 

standards or accepted definitions. To perform 

measurements under the same or very similar 

conditions by the participants it has been significant 

to agree on reference values of the influence 

parameters and testing cycles and realize them as 

much as possible to have more comparable 

reference systems.  

Table 4: Reference Values for Rockwell Hardness 

Scales HRA, HRBW and HRC 

 

In this comparison the reference values were 

chosen according to the HRC definition decided by 

the CIPM/CCM WGH [3]. Deviations from these 

values were taken into the uncertainty calculations. 

Table 4 includes the reference values and 

measurement cycle used in the HRA, HRBW and 

HRC measurements and Figure 4 shows the 

measurement cycle for HRA, HRBW and HRC. 

 

Figure 4: Identification of the HRA, HRBW and HRC 

Measurement Cycle [3] 

5. ELABORATION OF THE RESULTS  

As its being a supplementary comparison, there 

is no possibility to assign a reference value linked to 

an internationally accepted reference. In line with 

this situation, each laboratory recorded the 

measurement results and uncertainty values in the 

data sheet provided in the annex of the Technical 

Protocol for each hardness reference block. The 

pilot laboratory was responsible for collecting the 

measurement data from the participants, compiling, 

elaboration and preparing the reports. The 

measurement results were used to compute the 

Comparison Reference Value (CRV), degrees of 

equivalence (DoE) with the CRV and En ratios. The 

calculation is shown in following steps and made by 

making use of the following equations.  

• Calculation of the Comparison Reference 
Value (CRV) 

The pilot laboratory determined CRV by 

calculating the weighted mean of measurements of 

the two participants (𝑥𝑟𝑒𝑓 ) by making use of the 

following equation, 

𝑥𝑟𝑒𝑓 =
𝑥1 𝑢

2(𝑥1)⁄ + ⋯+ 𝑥𝑛 𝑢
2(𝑥𝑛)⁄

1 𝑢2(𝑥1)⁄ + ⋯+ 1 𝑢
2(𝑥𝑛)⁄

 (1) 

• The uncertainty of the CRV ( 𝑥𝑟𝑒𝑓 ) was 

calculated by the following expression, 

•  

1

𝑢2(𝑥𝑟𝑒𝑓)
=

1

𝑢2(𝑥1)
+ ⋯+

1

𝑢2(𝑥𝑛)
 (2) 

 

where,   

𝑥𝑖 : measured value of participating 
institute, i (i = 1, 2, ..., n) 

𝑢(𝑥𝑖) : standard uncertainty of 𝑥𝑖 

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ACTA IMEKO | www.imeko.org December 2020 | Volume 9 | Number 5 | 259 

𝑢(𝑥𝑟𝑒𝑓) : standard uncertainty of 𝑥𝑟𝑒𝑓 

• The deviation from the CRV is calculated 
by, 

𝑑𝑖 = 𝑥𝑖 − 𝑥𝑟𝑒𝑓 (3) 

• The uncertainty of this deviation at a 95% 
level of confidence is, 

𝑈(𝑑𝑖) = 𝑘 ∙ 𝑢(𝑑𝑖) (4) 

Where u(di ) is calculated by, 

𝑢2(𝑑𝑖) = 𝑢
2(𝑥𝑖) − 𝑢

2(𝑥𝑟𝑒𝑓) (5) 

and 𝑘 = 2. 
 

• The coefficient En is the equivalence between 
the measurements of participating institutes, 

is calculated as given below, 

𝐸𝑛 =
𝑥𝑖 − 𝑥𝑟𝑒𝑓

√𝑈2(𝑥𝑖) − 𝑈
2(𝑥𝑟𝑒𝑓)

 (6) 

where,  

𝑈(𝑥𝑖) = 𝑘 ∙ 𝑢(𝑥𝑖) (7) 

𝑈(𝑥𝑟𝑒𝑓) = 𝑘 ∙ 𝑢(𝑥𝑟𝑒𝑓) 
(8) 

• The xi is equivalent with xref (CRV) at 95% 
confidence level, if |𝐸n| ≤ 1, 

 

6. COMPARISON RESULTS  

In this comparison the degree of equivalence of 

each participant with respect to the CRV was 

calculated. This calculation comprises calculation 

the deviation of each participant from the CRV and 

the associated uncertainty of this deviation. Also the 

En ratios were also calculated for each hardness 

scale and level. The two participants declare 

consistent uncertainty values and measurements 

results are in a significant consistency with each 

other. Below you can see the tabular and graphical 

interpretation of the measurement results and 

calculations.  

Table 5: DoE of INRiM and UME (wrt. CRV) – HRA – 

common indenter 

 

Table 6: DoE of INRiM and UME (wrt. CRV) – HRBW 

– common indenter 

 

Table 7: DoE of INRiM and UME (wrt. CRV) – HRC – 

common indenter 

 

Table 8: DoE of INRiM and UME (wrt. CRV) – HRA – 

own indenter 

 

Table 9: DoE of INRiM and UME (wrt. CRV) – HRBW 

– own indenter 

 

Table 10: DoE of INRiM and UME (wrt. CRV) – HRC 

– own indenter 

 
 

In regard to the calculations shown in the tables 

above the graphical representations are as shown 

below. 

 
Figure 5: Deviations of INRiM and UME values from 

the CRV with the associated expanded uncertainty – 

HRA – common indenter 

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ACTA IMEKO | www.imeko.org December 2020 | Volume 9 | Number 5 | 260 

 
Figure 6: Deviations of INRiM and UME values from 

the CRV with the associated expanded uncertainty – 

HRBW – common indenter 

 
Figure 7: Deviations of INRiM and UME values from 

the CRV with the associated expanded uncertainty – 

HRC – common indenter 

 
Figure 8: Deviations of INRiM and UME values from 

the CRV with the associated expanded uncertainty – 

HRA – own indenter 

 
Figure 9: Deviations of INRiM and UME values from 

the CRV with the associated expanded uncertainty – 

HRBW – own indenter 

 
Figure 10: Deviations of INRiM and UME values from 

the CRV with the associated expanded uncertainty – 

HRC – own indenter 

7. SUMMARY 

At the end of the bilateral comparison between 

INRiM and UME in the most widely used Rockwell 

hardness scales HRA, HRBW and HRC is 

completed without any unexpected phenomena in 

any stage of it. The participating institutes declared 

similar uncertainty values and there was a 

significant consistency between the measured 

values of the transfer standards. The comparison 

reference values (CRVs), the deviation value of 

INRiM and UME from the CRV and their 

uncertainties, dINRiM, dUME, Ud-INRiM, Ud-UME, and En 

ratios were calculated and shown in Tables 5 to 10 

and Figures 5 to 10 in the Comparison Results. In 

some cases, the degrees of equivalence for the 

results obtained by the common indenter is greater 

than the degree of equivalence for the results 

obtained by the own indenters. This is probably 

because of a bias in our machine in that scale/range 

but still within the uncertainty declared. The degrees 

of equivalence show a significant consistency 

between INRiM and UME hardness standards in 

HRA, HRBW and HRC Rockwell hardness scales 

and this comparison is supporting the present and 

possible new CMC submissions.   

8. REFERENCES 

[1] EN ISO 6508–1:2016, Metallic Materials–Rockwell 
Hardness Test–Part1: Test Method (scales A, B, C, 

D, E, F, G, H, K, N, T). 

[2] EN ISO 6508–3:2015, Metallic Materials–Rockwell 
Hardness Test - Part3: Calibration of Reference 

Blocks (scales A, B, C, D, E, F, G, H, K, N, T). 

[3] https://www.bipm.org/wg/CCM/CCM-
WGH/Allowed/International_definitions/HRC_defi

nition.pdf 

[4] http://www.ltf.it/en/prodotti.php?b=3&c=636&p=3
361 

[5] EURAMET/cg–16/v.02, Guidelines on the 
Estimation of Uncertainty in Hardness 

Measurements, 2011. 

[6] JCGM 100:2008, Evaluation of measurement data–

Guide to the expression of uncertainty in 

measurement. 
 

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https://www.bipm.org/wg/CCM/CCM-WGH/Allowed/International_definitions/HRC_definition.pdf
https://www.bipm.org/wg/CCM/CCM-WGH/Allowed/International_definitions/HRC_definition.pdf
https://www.bipm.org/wg/CCM/CCM-WGH/Allowed/International_definitions/HRC_definition.pdf
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