SIST EN ISO 4545-2:2018
(Main)Metallic materials - Knoop hardness test - Part 2: Verification and calibration of testing machines (ISO 4545-2:2017)
Metallic materials - Knoop hardness test - Part 2: Verification and calibration of testing machines (ISO 4545-2:2017)
This document specifies the method of verification and calibration of testing machines for determining
Knoop hardness for metallic materials in accordance with ISO 4545-1.
A direct method of verification and calibration is specified for the testing machine, indenter, and the
diagonal length measuring system. An indirect verification method using reference blocks is specified
for the overall checking of the machine.
If a testing machine is also to be used for other methods of hardness testing, it will be verified
independently for each method.
Metallische Werkstoffe - Härteprüfung nach Knoop - Teil 2: Überprüfung und Kalibrierung der Prüfmaschinen (ISO 4545-2:2017)
In diesem Dokument ist das Verfahren für die Überprüfung und Kalibrierung von Härteprüfmaschinen zur Bestimmung der Knoop Härte von metallischen Werkstoffen nach ISO 4545 1 festgelegt.
Ein direktes Verfahren zur Prüfung und Kalibrierung der Härteprüfmaschine, des Eindringkörpers und des Diagnonalenmesssystems wird vorgegeben. Für die Gesamtprüfung der Maschine wird ein indirektes Prüfverfahren der Härteprüfmaschine angegeben.
Ist eine Prüfmaschine auch für andere Härteprüfverfahren vorgesehen, wird sie für jedes Verfahren einzeln geprüft.
Matériaux métalliques - Essai de dureté Knoop - Partie 2 : Vérification et étalonnage des machines d'essai (ISO 4545-2:2017)
ISO 4545-2:2017 spécifie une méthode de vérification et d'étalonnage des machines d'essai utilisées pour la détermination de la dureté Knoop pour les matériaux métalliques conformément à l'ISO 4545-1.
Une méthode directe de vérification et d'étalonnage est spécifiée pour la machine d'essais, le pénétrateur et le système de mesure de la longueur de la diagonale. Une méthode de vérification indirecte à l'aide de blocs de référence est spécifiée pour la vérification globale de la machine.
Si une machine d'essai est également utilisée pour d'autres méthodes d'essai de dureté, elle doit être vérifiée indépendamment pour chaque méthode.
Kovinski materiali - Preskus trdote po Knoopu - 2. del: Preverjanje in umerjanje naprav za preskušanje (ISO 4545-2:2017)
Ta del dokument določa metodo za preverjanje in umerjanje preskuševalnih naprav za določanje
trdote kovinskih materialov po Knoopu v skladu s standardom ISO 4545-1.
Določa neposredno metodo za preverjanje in umerjanje naprave za preskušanje, preskusne konice in sistema za merjenje dolžine diagonale. Za splošno pregledovanje naprave določa posredno metodo preverjanja z uporabo primerjalnih ploščic.
Če se naprava za preskušanje uporablja tudi za druge metode preskusa trdote, jo je treba preveriti posebej za vsako metodo.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 4545-2:2018
01-julij-2018
1DGRPHãþD
SIST EN ISO 4545-2:2006
Kovinski materiali - Preskus trdote po Knoopu - 2. del: Preverjanje in umerjanje
naprav za preskušanje (ISO 4545-2:2017)
Metallic materials - Knoop hardness test - Part 2: Verification and calibration of testing
machines (ISO 4545-2:2017)
Metallische Werkstoffe - Härteprüfung nach Knoop - Teil 2: Überprüfung und Kalibrierung
der Prüfmaschinen (ISO 4545-2:2017)
Matériaux métalliques - Essai de dureté Knoop - Partie 2 : Vérification et étalonnage des
machines d'essai (ISO 4545-2:2017)
Ta slovenski standard je istoveten z: EN ISO 4545-2:2018
ICS:
77.040.10 Mehansko preskušanje kovin Mechanical testing of metals
SIST EN ISO 4545-2:2018 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 4545-2:2018
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SIST EN ISO 4545-2:2018
EN ISO 4545-2
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2018
EUROPÄISCHE NORM
ICS 19.060; 77.040.10 Supersedes EN ISO 4545-2:2005
English Version
Metallic materials - Knoop hardness test - Part 2:
Verification and calibration of testing machines (ISO 4545-
2:2017)
Matériaux métalliques - Essai de dureté Knoop - Partie Metallische Werkstoffe - Härteprüfung nach Knoop -
2: Vérification et étalonnage des machines d'essai (ISO Teil 2: Überprüfung und Kalibrierung der
4545-2:2017) Prüfmaschinen (ISO 4545-2:2017)
This European Standard was approved by CEN on 30 November 2017.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4545-2:2018 E
worldwide for CEN national Members.
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SIST EN ISO 4545-2:2018
EN ISO 4545-2:2018 (E)
Contents Page
European foreword . 3
2
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SIST EN ISO 4545-2:2018
EN ISO 4545-2:2018 (E)
European foreword
This document (EN ISO 4545-2:2018) has been prepared by Technical Committee ISO/TC 164
“Mechanical testing of metals” in collaboration with Technical Committee ECISS/TC 101 “Test methods
for steel (other than chemical analysis)” the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by September 2018, and conflicting national standards
shall be withdrawn at the latest by September 2018.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 4545-2:2005.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 4545-2:2017 has been approved by CEN as EN ISO 4545-2:2018 without any
modification.
3
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SIST EN ISO 4545-2:2018
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SIST EN ISO 4545-2:2018
INTERNATIONAL ISO
STANDARD 4545-2
Second edition
2017-12
Metallic materials — Knoop
hardness test —
Part 2:
Verification and calibration of testing
machines
Matériaux métalliques — Essai de dureté Knoop —
Partie 2: Vérification et étalonnage des machines d'essai
Reference number
ISO 4545-2:2017(E)
©
ISO 2017
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SIST EN ISO 4545-2:2018
ISO 4545-2:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved
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SIST EN ISO 4545-2:2018
ISO 4545-2:2017(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General conditions . 1
5 Direct verification . 2
5.1 General . 2
5.2 Calibration of the test force . 2
5.3 Verification of the indenter . 3
5.4 Calibration and verification of the diagonal measuring system . 4
5.5 Verification of the testing cycle . 4
5.6 Uncertainty of calibration/verification . 5
6 Indirect verification . 5
6.1 General . 5
6.2 Test force and hardness levels . 5
6.3 Measurement of reference indentations. 5
6.4 Number of indentations . 5
6.5 Verification result . 5
6.6 Repeatability . 6
6.7 Bias . 6
6.8 Uncertainty of calibration/verification . 7
7 Intervals between verifications . 7
8 Verification report/calibration certificate . 7
8.1 Knoop testing machine . 7
8.2 Knoop indenter . 8
Annex A (informative) Uncertainty of the calibration results of the hardness testing system .9
Bibliography .18
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SIST EN ISO 4545-2:2018
ISO 4545-2:2017(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals,
Subcommittee SC 3, Hardness testing.
This second edition cancels and replaces the first edition (ISO 4545-2:2005), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— all references have been removed of indentation diagonals <0,020 mm;
— the requirements for the calibration and verification of the measuring system have been revised;
— the requirements for the maximum permissible error in measuring a reference indentation have
been revised;
— the recommendations for inspection and monitoring of the indenter have been moved to ISO 4545-1;
— Annex A has been revised.
A list of all parts in the ISO 4545 series can be found on the ISO website.
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SIST EN ISO 4545-2:2018
INTERNATIONAL STANDARD ISO 4545-2:2017(E)
Metallic materials — Knoop hardness test —
Part 2:
Verification and calibration of testing machines
1 Scope
This document specifies the method of verification and calibration of testing machines for determining
Knoop hardness for metallic materials in accordance with ISO 4545-1.
A direct method of verification and calibration is specified for the testing machine, indenter, and the
diagonal length measuring system. An indirect verification method using reference blocks is specified
for the overall checking of the machine.
If a testing machine is also to be used for other methods of hardness testing, it will be verified
independently for each method.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 376:2011, Metallic materials — Calibration of force-proving instruments used for the verification of
uniaxial testing machines
ISO 4545-1, Metallic materials — Knoop hardness test — Part 1: Test method
ISO 4545-3, Metallic materials — Knoop hardness test — Part 3: Calibration of reference blocks
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
4 General conditions
Before a Knoop hardness testing machine is verified, it shall be checked to ensure that it is properly set
up in accordance with the manufacturer's instructions.
Especially, it should be checked that
a) the plunger holding the indenter is capable of moving freely without any friction or excessive
side play,
b) the indenter is firmly mounted in the plunger,
c) the test force can be applied and removed without shock, vibration, or overload, and in such a
manner that the readings are not influenced, and
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SIST EN ISO 4545-2:2018
ISO 4545-2:2017(E)
d) the diagonal measuring system
— if integral with the machine, the change in mode from the application and removal of the test
force to the diagonal measuring mode does not influence the readings,
— the illumination device of the measuring microscope produces uniform lighting of the whole
observed field with enough contrast between the indentation and the surrounding surface to
determine the boundary clearly, and
— the centre of the indentation is near the centre of the field of view, if necessary.
NOTE The criteria specified in this document for the performance of the testing machine have been
developed and refined over a significant period of time. When determining a specific tolerance that the machine
needs to meet, the uncertainty associated with the use of measuring equipment and/or reference standards has
been incorporated within this tolerance, and it would therefore be inappropriate to make any further allowance
for this uncertainty by, for example, reducing the tolerance by the measurement uncertainty. This applies to all
measurements made when performing a direct or indirect verification of the machine.
5 Direct verification
5.1 General
5.1.1 Direct verification shall be conducted in accordance with the schedule given in Clause 7.
5.1.2 Direct verification involves
a) the calibration of the test force,
b) the verification of the indenter,
c) the calibration and verification of the diagonal measuring system, and
d) the verification of the testing cycle.
5.1.3 Direct verification should be carried out at a temperature of (23 ± 5) °C. If the verification is
carried out at a temperature outside this range, this shall be stated in the verification report.
5.1.4 The instruments used for verification and calibration shall be traceable to national standards.
5.2 Calibration of the test force
5.2.1 Each test force to be used within the force range of the testing machine shall be measured.
Whenever the indenter position affects the applied force, this shall be done at not less than three
positions of the plunger uniformly spaced throughout its range of movement during testing.
For testing machines whose test force is shown not to be influenced by the position of the plunger, e.g.
closed-loop controlled loading system, the test force can be calibrated in one position.
5.2.2 The test force shall be measured by one of the following two methods:
— by means of an elastic proving device in accordance with ISO 376:2011, class 1, or better;
— by balancing against a force, accurate to ±0,2 %, applied by means of calibrated masses or another
method with the same accuracy.
Evidence should be available to demonstrate that the output of the force-proving device does not vary
by more than 0,2 % in the period of 1 s to 30 s following a stepped change in force.
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SIST EN ISO 4545-2:2018
ISO 4545-2:2017(E)
5.2.3 Three readings shall be taken for each test force, F, at each position of the plunger. Immediately
before each reading is taken, the indenter shall be moved in the same direction as during the test. All
readings shall be within the maximum permissible percent relative error, ∆F , defined in Table 1.
rel
The percent relative error, ∆F , of each measurement of the force, F, is calculated according to
rel
Formula (1):
FF−
RS
ΔF =×100 (1)
rel
F
RS
where
F is the measured test force;
F is the nominal test force.
RS
Table 1 — Test force tolerances
Range of the nominal test force, Maximum permissible relative
F error, ∆F
RS rel
N %F
0,009 807 ≤ F < 0,098 07 ±2,0
RS
0,098 07 ≤ F < 1,961 ±1,5
RS
1,961 ≤ F ≤ 19,613 ±1,0
RS
5.3 Verification of the indenter
5.3.1 The four faces of the diamond pyramid shall be polished and free from surface defects.
5.3.2 The verification of the shape of the indenter can be made by direct measurement or optical
measurement. The device used for the verification shall have a maximum expanded uncertainty of 0,07°.
5.3.3 The measured angle α between the opposite edges at the vertex of the diamond pyramid shall be
within the range (172,5 ± 0,1)°(see Figure 1).
5.3.4 The measured angle β between the opposite edges at the vertex of the diamond pyramid shall be
within the range (130 ± 1,0)° (see Figure 1).
5.3.5 The indenter constant c (see ISO 4545-1:2018, Table 1) shall be within 1,0 % of the ideal value
0,070 28, (0,069 58 ≤ c ≤ 0,070 98).
NOTE To achieve the tolerances for the indenter constant, c, the values of angle α and/or angle β can be kept
to closer tolerances than given above.
5.3.6 The angle between the axis of the diamond pyramid and the axis of the indenter holder (normal
to the seating surface) shall be within ±0,5°.
5.3.7 The four faces should ideally meet at a common point; however, there is usually a line of junction
between opposite faces as shown in Figure 2. The length of the line of junction shall be determined by
directly measuring the indenter tip, or by measuring the tip impression in an indentation. The maximum
permissible length of the line of junction between opposite faces shall be less than 0,001 mm.
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SIST EN ISO 4545-2:2018
ISO 4545-2:2017(E)
5.3.8 A valid calibration certificate shall exist which confirms the geometrical deviations of the
indenter (see 8.2).
Figure 1 — Indenter geometry
Dimensions in micrometres
Figure 2 — Line of junction on the top of the indenter (schematic)
5.4 Calibration and verification of the diagonal measuring system
5.4.1 The system for measuring the diagonal of the indentation shall be verified at each magnification
and for each incorporated line scale to be used. When an individual scale is used in two perpendicular
axes, it shall be calibrated in both orientations. Measurements shall be performed using a calibrated
stage micrometer. The maximum expanded uncertainty of the distances between the line intervals on the
stage micrometer shall be as indicated in Table 2.
5.4.2 Measurements shall be made at a minimum of four evenly spaced intervals, arranged centrally in
the field of view, covering each working range. Three measurements shall be made at each of the evenly
spaced intervals. The maximum permissible error of each of the three measurements at each interval
shall be as indicated in Table 2.
Table 2 — Calibration and verification requirements of the measuring system
Calibration and verification
Measurement parameters
requirements
Maximum expanded uncertainty of the distances
Greater of 0,000 4 mm
between the line intervals on the stage micrometer
or 0,2 %
(see 5.4.1)
Maximum permissible error of the measurements of the stage
Greater of 0,000 8 mm
micrometer intervals
or 1,0 % of the length measured
(see 5.4.2)
5.5 Verification of the testing cycle
The testing cycle shall be timed with equipment having a maximum expanded uncertainty of 1 s. The
timing values obtained shall fall within the limits set for the testing cycle in ISO 4545-1.
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SIST EN ISO 4545-2:2018
ISO 4545-2:2017(E)
5.6 Uncertainty of calibration/verification
Uncertainty of the direct verification results shall be determined. An example is given in Annex A.
6 Indirect verification
6.1 General
6.1.1 Indirect verification shall be conducted in accordance with the schedule given in Clause 7.
6.1.2 Indirect verification involves verification of the overall performance of the testing machine by
means of reference blocks calibrated in accordance with ISO 4545-3.
6.1.3 Indirect verification should be carried out at a temperature of (23 ± 5) °C. If the verification is
made outside this temperature range, this shall be reported in the verification report.
6.1.4 The instruments used for verification and calibration shall be traceable to national standards.
6.2 Test force and hardness levels
The testing machine shall be verified by testing reference blocks that have been calibrated in accordance
with ISO 4545-3. The blocks shall have been calibrated using the same test forces that the machine will
use for future testing. When verifying more than one test force, at least two reference blocks shall be
selected from the hardness ranges specified below for each test force that the machine will be verified.
The set of blocks needed for verifying the machine for all the test forces shall be chosen so that at least
one reference block from each hardness range is used for the verifications. When verifying testing
machines using only one test force, three reference blocks shall be used, one from each of the three
hardness ranges specified below. The hardness ranges should be chosen, when possible, to replicate the
hardness levels most commonly tested when using the specific test forces:
— <250 HK;
— 250 HK to 650 HK;
— >650 HK.
6.3 Measurement of reference indentations
One of the reference indentations from the current calibration period on each reference block shall be
measured. For each indentation, the difference between the measured value and the certified diagonal
length shall not exceed the greater of 0,001 mm and 1,25 % of the reference indentation length. If
preferred, this check may instead be made on a similarly-sized indentation in a different reference
block with similar hardness.
6.4 Number of indentations
On each reference block, five indentations shall be made and measured. The tests shall be carried out
in accordance with ISO 4545-1. Only the calibrated surfaces of the test blocks are to be used for testing.
6.5 Verification result
For each reference block, let H , H , H , H , H be the measured hardness arranged in increasing order
1 2 3 4 5
of magnitude, corresponding to the measured diagonals d , d , d , d , d in decreasing order of
1 2 3 4 5
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SIST EN ISO 4545-2:2018
ISO 4545-2:2017(E)
magnitude. The mean hardness value, H , is calculated according to Formula (2), and the mean diagonal
length, d , is calculated according to Formula (3):
HHH++ ++HH
12 34 5
H = (2)
5
ddd++ ++dd
12 34 5
d= (3)
5
6.6 Repeatability
The relative repeatability of the testing machine, r expressed as a percentage of H , is calculated
rel,
according to Formula (4):
HH−
51
r =×100 (4)
rel
H
The repeatability of the testing machine is satisfactory if (d – d ) ≤ 0,001 mm. If (d – d ) > 0,001 mm,
1 5 1 5
the testing machine is satisfactory if r is less than or equal to the percentages indicated in Table 3.
rel
Table 3 — Maximum permissible relative repeatability
Maximum permissible relative HK repeatability
of the testing machine, r
Knoop hardness of the rel
%HK
reference block
HK 0,5 to HK 2 HK 0,001 to
100 ≤ HK ≤ 250 16,0 18,0
250 < HK ≤ 650 10,0 10,0
HK > 650 8,0 8,0
NOTE Lower hardness materials often exhibit higher values of repeatability than those
for higher hardness materials.
6.7 Bias
The bias, b, of the testing machine under the particular verification conditions is calculated according
to Formula (5):
bH=−H (5)
CRM
where
H is the certified hardness of the reference block used.
CRM
The percent bias, b , is calculated according to Formula (6):
rel
HH−
CRM
b =×100 (6)
rel
H
CRM
The maximum positive or negative bias of the testing machine, expressed as a percentage of the
specified hardness of the reference block, shall not exceed the values given in Table 4.
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SIST EN ISO 4545-2:2018
ISO 4545-2:2017(E)
Table 4 — Maximum permissible percent HK bias
Mean diagonal length Maximum permissible
percent HK bias, b ,
rel
d
of the testing machine,
mm
± %HK
0,02 ≤ d < 0,06 0,24/ d
4
0,06 ≤ d
6.8 Uncertainty of calibration/verification
The uncertainty of the calibration results shall be determined. An example is given in Annex A.
7 Intervals between verifications
Direct verifications shall be performed according to the schedule given in Table 5. It is recommended
that direct verifications be performed every 12 months.
Indirect verification shall be performed at least once every 12 months and after a direct verification
has been performed.
Table 5 — Direct verifications of hardness testing machines
Diagonal
a
Requirements of verification Force measuring Test cycle Indenter
system
Before setting to work first time x x x x
After dismantling and reassembling,
if force, diagonal measuring system or x x x —
test cycle are affected
b
Failure of indirect verification x x x —
Indirect verification > 13 months ago x x x —
a
In addition, it is recommended that the indenter be directly verified after two years of use.
b
Direct verification of these parameters may be carried out sequentially (until the machine passes indirect verification)
and is not required if it can be demonstrated (e.g. by tests with a reference indenter) that the indenter was the cause of the
failure.
8 Verification report/calibration certificate
8.1 Knoop testing machine
Th
...
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