ISO 2321:2006
(Main)Rubber threads — Methods of test
Rubber threads — Methods of test
ISO 2321:2006 specifies methods of test for determining general physical and mechanical properties of rubber threads, as well as specific mechanical properties of such threads in contact with fabrics. Owing to the comparatively small cross-section and the unusual conditions of service of this material, certain special methods have been developed. Some of the tests included in this International Standard may not be entirely suitable for threads made from certain synthetic rubbers (e.g. urethane rubber). These tests are intended for natural or synthetic polyisoprene rubbers.
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INTERNATIONAL ISO
STANDARD 2321
Third edition
2006-11-15
Rubber threads — Methods of test
Fils élastiques — Méthodes d'essai
Reference number
ISO 2321:2006(E)
©
ISO 2006
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ISO 2321:2006(E)
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ISO 2321:2006(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Conditioning of samples or test pieces. 1
4 Count. 2
5 Metric yield . 4
6 Properties of rubber threads . 5
7 Density . 5
8 Tensile strength, modulus and elongation at break . 7
9 Schwartz value (SV). 8
10 Elongation under a specified load . 9
11 Stress retention. 11
12 Accelerated-ageing test on rubber threads in a relaxed state. 13
13 Dry-heat resistance. 14
14 Ribbons: Degree of adhesion between threads . 16
15 Resistance to copper staining during laundering. 17
16 Effect of washing . 20
17 Resistance to atmospheric fume staining. 22
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ISO 2321:2006(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 2321 was prepared by Technical Committee ISO/TC 45, Rubber and rubber products, Subcommittee
SC 4, Products (other than hoses).
This third edition cancels and replaces the second edition (ISO 2321:1983), which has been technically
revised.
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INTERNATIONAL STANDARD ISO 2321:2006(E)
Rubber threads — Methods of test
1 Scope
This International Standard specifies methods of test for determining general physical and mechanical
properties of rubber threads, as well as specific mechanical properties of such threads in contact with fabrics.
Owing to the comparatively small cross-section and the unusual conditions of service of this material, certain
special methods have been developed.
Some of the tests included in this International Standard may not be entirely suitable for threads made from
certain synthetic rubbers (e.g. urethane rubber). These tests are intended for natural or synthetic polyisoprene
rubbers.
It is pointed out that comparisons may only be made on new rubber threads or on those with identical
processing histories. In the interpretation of results from threads which have been subjected to spooling,
fabrication or any other process, it should be borne in mind that the previous history is important, and what is
known of this and of any relaxation treatments used shall be stated in the test report.
2 Normative references
The following referenced documents are indispensable for the application 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 37, Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties
ISO 105-A02, Textiles — Tests for colour fastness — Part A02: Grey scale for assessing change in colour
ISO 105-A03, Textiles — Tests for colour fastness — Part A03: Grey scale for assessing staining
ISO 188, Rubber, vulcanized or thermoplastic — Accelerated ageing and heat resistance tests
ISO 648, Laboratory glassware — One-mark pipettes
ISO 1042, Laboratory glassware — One-mark volumetric flasks
ISO 1183-2, Plastics — Methods for determining the density of non-cellular plastics — Part 2: Density gradient
column method
ISO 23529, Rubber — General procedures for preparing and conditioning test pieces for physical test
methods
3 Conditioning of samples or test pieces
The samples or test pieces shall be kept in a relaxed state in one of the standard atmospheres described in
ISO 23529, for not less than 16 h before testing. The tests shall be carried out under similar atmospheric
conditions. The test piece selected shall be clean, dry and free from any visual defects. Samples or test
pieces shall not be allowed to come into contact with copper or manganese or their compounds during
conditioning or testing.
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ISO 2321:2006(E)
4 Count
4.1 Sectional count
The sectional count of a rubber thread is given by the value of its cross-sectional area, expressed in square
millimetres.
3 3
NOTE The sectional count corresponds to the tex count for a nominal density of 1 Mg/m (= 1g/cm ). The use of the
sectional count is recommended.
4.2 Conventional count (size number)
4.2.1 The conventional count of a rubber thread is the number of threads which, when placed side by side,
measure 25,4 mm.
The conventional count of a round thread is calculated by dividing 25,4 by the diameter, in millimetres, of the
thread.
The conventional count of a square thread is calculated by dividing 25,4 by the length, in millimetres, of one of
the sides of the thread.
The conventional count of a rectangular thread is generally quoted as the count of a square thread of
equivalent cross-sectional area.
Thus, in the case of a round thread, the number 100 is the conventional count of a thread whose diameter is
equal to 0,254 mm; in the case of a square thread, the number 40 is the conventional count of a thread whose
sides are equal to 0,635 mm.
4.2.2 It is customary to quote the conventional count of a round thread, followed by the whole even number
which is nearest to the actual conventional count of the square thread of equivalent cross-sectional area
(count of round thread × 1,13 = actual count of square thread).
EXAMPLE A round thread of count 50 is indicated by 50/56.
4.2.3 The conventional count of a multi-filament round thread is expressed by stating successively the
number of components, the count of the single round thread which would have the same total cross-sectional
area as the component threads, and the count of the corresponding square thread.
EXAMPLE The conventional count of a multi-filament round thread made up of three components equal in total
cross-sectional area to a round thread of count 32 is indicated by 3/32/36.
4.3 Apparatus
See Figure 1.
The apparatus for cutting the test pieces consists of a rectangular vertical frame at the upper and lower ends
of which are mounted two metal plates whose inside edges are parallel and sharp. Two cutting devices (the
fixed blade of which consists of the inside edge of the metal plate) and two external clamps are provided. The
clamps shall be of a spring-loaded type and the distance between the internal edges of the metal plates shall
be 100 mm ± 1 mm.
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ISO 2321:2006(E)
Key
1 metal plate
2 clamp
3 cutting device
Figure 1 — Apparatus for cutting test pieces
4.4 Procedure
4.4.1 Cutting out the test pieces
Take five strips of thread samples and cut them to a length of approximately 110 mm.
Tear off threads equally from both edges of each strip till there are only ten threads in each strip. If these
strips are taken from bobbins or from any other type of presentation in which the strip is under tension, heat-
treat them for 30 min in a thermostatically controlled oven at a temperature of 70 °C ± 2 °C. After this heat
treatment, condition the strips as specified in Clause 3. For strips taken from other forms of presentation
where no tension is applied to the strip, condition as specified in Clause 3.
Suspend each conditioned strip from the upper clamp. When it has settled in the vertical position without
stretch, fix it by means of the lower clamp. Cut the strip to the required length with the two cutting devices,
using the lower one first.
4.4.2 Weighing the test pieces
Free the cut strips from any loose dusting powder by shaking or brushing them gently and weigh to an
accuracy of ± 1 %.
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ISO 2321:2006(E)
4.5 Expression of results
4.5.1 The sectional count, S, is given by the equation:
m 1
S=×
ρ 1000
where
ρ is the density, expressed in megagrams per cubic metre, of the thread, determined as specified in
Clause 7;
m is the mass, in milligrams, of the strip.
4.5.2 The conventional count, C, is given by the following equations:
For round thread
ρ
C= 22,51
m
For square thread
ρ
C= 25,40
m
where
ρ is the density, expressed in megagrams per cubic metre, of the thread, determined as specified in
Clause 7;
m is the mass, in milligrams, of the strip.
4.5.3 Express the count of the thread as the median of the values for the five test pieces as indicated in
4.2.3. The maximum and minimum values obtained shall also be stated.
5 Metric yield
5.1 Terms and definitions
For the purposes of this clause, the following terms and definitions apply.
5.1.1
metric yield
unstretched length, in metres, of 1 000 g of thread
5.2 Procedure
Determine the mass of each of five test pieces as specified in 4.4.2.
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ISO 2321:2006(E)
5.3 Expression of results
5.3.1 The metric yield of rubber thread, expressed in metres per kilogram, is given by the formula:
1000
m
where m is the mass, in grams, of 1 000 mm of thread.
5.3.2 Express the metric yield of the thread as the median of the values for the five test pieces.
6 Properties of rubber threads
Properties of rubber threads are made up of two kinds: general physical and mechanical properties, and
specific mechanical properties of the threads in contact with fabrics. They shall be determined by the test
methods specified in Table 1 and Table 2, respectively.
Table 1 — General properties of rubber threads
Physical and mechanical properties Clause No.
Density 7
Tensile strength, modulus, elongation at break 8
Schwartz value (SV) 9
Elongation under a specified load 10
Stress retention 11
Accelerated-ageing test on rubber threads in a relaxed state 12
Dry-heat resistance test 13
Table 2 — Specific properties of rubber threads
Mechanical properties in contact with fabrics Clause No.
Ribbons: Degree of adhesion between threads 14
Resistance to copper staining during laundering 15
Effect of washing 16
Resistance to atmospheric fume staining 17
7 Density
7.1 Terms and definitions
For the purposes of this clause, the following terms and definitions apply.
7.1.1
density (of thread)
mass per unit volume of a test piece of thread measured at a standard laboratory temperature and expressed
in megagrams per cubic metre
NOTE The standard laboratory temperatures are given in ISO 23529.
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ISO 2321:2006(E)
7.2 Principle
Test pieces are placed in a suitable mixture of liquids, the density of which is adjusted until the test pieces
neither float nor sink; this density is determined.
7.3 Methods
7.3.1 Method A
3
7.3.1.1 Most of the rubber threads on the market have a density in the range of 0,90 Mg/m to
3
1,11 Mg/m . It is necessary, therefore, to have a series of liquids having densities within this range. Mixtures
3 3
of ethanol (0,79 Mg/m ) and ethylene glycol (1,11 Mg/m ) are suitable.
For threads of greater density, a suitable inorganic salt solution may be used. A solution of sodium chloride is
suitable.
7.3.1.2 Before the mixtures are used, it shall be ensured that they are homogeneous and free from air
bubbles. They shall be kept in closed containers so as to avoid evaporation. They shall be used at a
temperature of 20 °C ± 2 °C.
7.3.1.3 Apparatus
3
7.3.1.3.1 Glass cylinder, of capacity about 1 000 cm .
7.3.1.3.2 Hydrometer or hydrostatic balance or other apparatus allowing measurement of the density of
3
liquids to an accuracy of at least 0,005 Mg/m .
7.3.1.4 Procedure
7.3.1.4.1 Take four test pieces approximately 10 mm long from the sample. Dip each test piece in ethanol
and then rub between the fingers to remove dusting powder and any air bubbles from the surface.
7.3.1.4.2 Take a suitable liquid mixture (see 7.3.1.1) and thoroughly homogenize it, taking care not to
introduce any air bubbles. Place one of the test pieces in the liquid. Adjust the density of the liquid by addition
of the appropriate component, mixing thoroughly after each addition. Continue this adjustment until the test
piece neither sinks nor floats.
7.3.1.4.3 Test the other three test pieces in the mixture; at least two of these three test pieces shall reach
equilibrium within a period of 3 min to 10 min.
3
7.3.1.4.4 Determine the density of the liquid mixture to the nearest 0,005 Mg/m .
7.3.2 Method B
Determine the density of the test pieces in accordance with ISO 1183-2.
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ISO 2321:2006(E)
8 Tensile strength, modulus and elongation at break
8.1 Terms and definitions
For the purposes of this clause, the following terms and definitions apply.
8.1.1
tensile strength
stress at which the thread breaks when it is stretched under specified conditions, the value being expressed in
1)
megapascals , based on the initial cross-sectional area
8.1.2
modulus at 300 % and 500 %
1)
stress, measured in megapascals , calculated with respect to the original cross-sectional area, at 300 % and
500 % elongation
8.1.3
elongation at break
increase in length of the thread at break when it is stretched under the specified conditions, expressed as the
percentage increase in the original length
EXAMPLE A test piece 30 mm in length which increases in length to 210 mm at break is said to give an elongation
at break of 600 %.
8.2 Apparatus
8.2.1 Loop-forming machine.
8.2.2 Tensile-testing machine, as described in ISO 37, with O-ring grips.
8.3 Procedure
8.3.1 Test piece preparation
The thread test piece is allowed to relax at room temperature for 60 min to ensure that all stresses in the
thread have been released. It is then weighed and the average diameter of the thread calculated.
Using a loop-forming machine, the rubber thread is made into a loop and the ends tied securely. The diameter
of the loop is dependent on the distance between the two cylinders of the tensile-testing machine (see 8.3.2).
Usually, these are set 100 mm apart. The total number of loops for each test piece is dependent on the count
of the thread and the load capacity of the tensile tester. The more loops, the greater the total cross-sectional
area and hence the greater the force which will be needed to stretch the test piece to breaking point.
8.3.2 The test piece is looped over the two cylinders of the tensile tester. The loop diameter shall be such
that it fits exactly over the two cylinders without stretching.
The tensile tester is then run to stretch the test piece to breaking point. The machine is set to read the
modulus at 300 % and 500 %, the tensile strength and the elongation at break. Depending on the complexity
of the machine, usually the cross-sectional area of the loop is entered into the machine and the modulus and
tensile strength are then automatically calculated and printed out on a printer or displayed on a computer
screen. The elongation at break, calculated as the percentage stretch relative to the original length (100 mm),
is automatically displayed by the tensile tester on completion of the test.
Test five test pieces.
2
1) 1 MPa = 1N/mm
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ISO 2321:2006(E)
8.4 Expression of results
2
Modulus at 300 % (in mN/mm ) = F /A
300
2
Modulus at 500 % (in mN/mm ) = F /A
500
2
Tensile strength (in mN/mm ) = F /A
B
LL−
B0
Elongation at break (in %) = ×100
L
0
where
F is the force, in millinewtons, necessary to stretch the test piece to 300 %;
300
F is the force, in millinewtons, necessary to stretch the test piece to 500 %;
500
F is the force, in millinewtons, necessary to stretch the test piece to the break point;
B
A is the total cross-sectional area, in square millimetres, of the test piece.
L is the length at break of the test piece;
B
L is the original length of the test piece.
0
Express the tensile strength, modulus and elongation at break of the thread as the median of the values for
the five test pieces. The maximum and minimum values shall also be quoted. In addition, the test report shall
indicate the type of apparatus used and the procedure followed.
9 Schwartz value (SV)
9.1 Terms and definitions
For the purposes of this clause, the following terms and definitions apply.
9.1.1
Schwartz value
average of the stresses, in megapascals, calculated with respect to the original cross-sectional area at a
specified elongation measured on extension and retraction of a previously massaged (mechanically
conditioned) thread
c
NOTE 1 It is denoted by the abbreviated term SV , where c is the massaging elongation (the elongation to which the
n
test piece is stretched during mechanical conditioning) and n the elongation at which the readings are taken. Both c and n
are expressed as percentages of the initial length as multiples of 100 and, unless otherwise specified, are chosen so that
c = n + 100
NOTE 2 The preferred values of n are 300 % and 500 %, depending on the type of thread under test.
9.1.2
Schwartz hysteresis ratio
ratio of the loads at a specified elongation measured on extension and retraction, after massaging
(mechanical conditioning)
c
NOTE 1 It is denoted by the abbreviated term SHR , where c is the massaging elongation (the elongation to which the
n
test piece is stretched during mechanical conditioning) and n the elongation at which readings are taken. Both c and n are
expressed as percentages of the initial length as multiples of 100 and, unless otherwise specified, are chosen so that
c = n + 100
NOTE 2 The preferred values of n are 300 % and 500 %, depending on the type of thread under test.
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ISO 2321:2006(E)
9.2 Apparatus
The apparatus described in 8.2 may be used.
9.3 Procedure
Prepare three test pieces each consisting of a loop, or a multiple loop, of thread, the length of the loop being
100 mm ± 1 mm and the number of turns being selected to suit the count of the thread and the capacity of the
apparatus.
With a multiple loop, distribute the thread evenly between the turns by rotating the loop around the fingers
before placing it over the O-ring grips.
Carry out six cycles of elongation and retraction without interruption to an elongation of c %. On the sixth cycle,
take readings at n % elongation (during extension and again during retraction). Minimal pauses to take
readings are permissible.
9.4 Expression of results
c c
The Schwartz value, SV , in megapascals, and the Schwartz hysteresis ratio, SHR , expressed as a
n n
percentage, are given by the equations:
F +F
c
12
SV =
n
4SN
F
c
2
SHR=×100
n
F
1
where
F is the load, in meganewtons, at n % elongation on extension (6th cycle);
1
F is the load, in meganewtons, at n % elongation on retraction (6th cycle);
2
S is the original cross-sectional area, in square metres, of the test piece;
N is the number of complete loops tested.
Express the Schwartz value and Schwartz hysteresis ratio of the thread as the median of the values obtained
for the three test pieces. The test report shall also indicate the type of apparatus used and the procedure
followed.
10 Elongation under a specified load
10.1 Terms and definitions
For the purposes of this clause, the following terms and definitions apply.
10.1.1
elongation under specified load
percentage elongation of a rubber thread when stressed by the application of a specified load per unit area
NOTE 1 It is determined by applying a load to an unmassaged thread (i.e. a thread which has not been mechanically
conditioned) and so is liable to be affected by the age and previous history (including storage history and any conditioning)
of the thread.
2
NOTE 2 It is normally determined at two levels of applied force: 15,5 kPa (= 15,5 mN/mm ) and 27,4 kPa
2
(= 27,4 mN/mm ).
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ISO 2321:2006(E)
10.2 Test pieces
Use one or more pieces of thread, depending on the count, as the test piece. The length will depend on the
apparatus used.
10.3 Apparatus
10.3.1 The essential requirements are that the apparatus is capable of stretching a test piece at a constant
speed until the load reaches a predetermined value, and that it incorporates a graduated scale for reading the
elongation.
10.3.2 A suitable apparatus is shown in Figure 2. It consists of:
a) A graduated scale for reading the elongation of the test piece.
b) Two clamps for gripping the ends of the test piece, the length between the clamps in the initial state being
150 mm ± 2 mm, together with a means of mechanically moving the upper clamp in a vertical direction to
extend the test piece at a constant speed of 30 mm/s ± 10 mm/s.
c) A pan, attached to the lower clamp, to which the necessary weights may be added to make up the load
appropriate to the count of the thread being tested.
d) An electric switch, situated immediately beneath the pan. When the weight of the pan is exceeded by the
force exerted on it by the stretched thread, the pan is lifted and the switch stops the motor and applies the
brake.
If, for this test, an apparatus differing from that described above but complying with 8.2 is used, the test report
shall state the type of apparatus used and the procedure followed.
Key
1 graduated scale 3 pan for weights
2 clamps 4 electric switch
Figure 2 — Apparatus for determination of elongation under a specified load
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ISO 2321:2006(E)
10.4 Procedure
Prepare three test pieces of the kind specified in 10.2. Fix the ends of the first test piece in the clamps so that
the test piece is taut but unstretched, and add the required weights to the pan. Start the motor and, when it is
automatically stopped by the switch, measure the elongation of the test piece on the scale. Repeat the
procedure for the other two test pieces.
10.5 Expression of results
10.5.1 The elongation, A, expressed as a percentage, of the test piece under the specified load is given by
the equation:
LL−
t0
A=×100
L
0
where
L is the original length, in millimetres, of the test piece;
0
L is the total length, in millimetres, of the extended test piece.
t
10.5.2 Express the elongation under specified load as the median of the values for the three test pieces.
11 Stress retention
11.1 Terms and definitions
For the purposes of this clause, the following terms and definitions apply.
11.1.1
stress retention
residual load, expressed as a percentage of the original load on the thread, after the test piece has been
maintained at a constant elongation (usually 100 %) for a specified time
11.2 Test pieces
Test pieces shall consist of loops of the type described in 9.3.
11.3 Apparatus
Figure 3 shows a simple apparatus for carrying out this test. One end of the test piece is passed round one
peg, the other end being attached to the other peg by means of a wire clip. A spring dynamometer is attached
to the other end of the wire clip and the load required to just lift the clip off the peg measured. The distance
between the two pegs shall be such that the thread is subjected to the specified elongation to within ± 2 %.
11.4 Procedure
11.4.1 Prepare three test pieces of the kind specified in 11.2. Pass the end of each test piece round the
bottom peg and attach the other end to the wire clip as shown in Figure 3. Then pass the inner loop of the wire
clip over the top peg, thus subjecting the test piece to the specified elongation with an accuracy of ± 2 %
[usually (100 ± 2) %]. Maintain this extension during the test.
11.4.2 When a measurement of stress is to be made, attach the spring dynamometer to the outer loop of the
wire clip and raise the dynamometer until the wire clip is just clear of its supporting peg. At this point, read the
dynamometer, which just counterbalances the force exerted on the rubber thread.
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ISO 2321:2006(E)
11.4.3 Take the initial reading 30 min ± 1 min after the initial extension of the thread on the apparatus.
Continue to take readings as required up to a maximum of 14 days.
11.4.4 The test may be carried out at ambient or elevated temperatures. The test conditions used and the
duration of the test shall be stated in the test report.
Key
1 spring dynamometer
2 pegs
3 wire clip
Figure 3 — Apparatus for determination of stress retention
11.5 Expression of results
11.5.1 The stress retention, expressed as a percentage, of the test piece, is given by the formula:
F
2
×100
F
1
where
F is the original load;
1
F is the residual load.
2
11.5.2 Express the str
...
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