ASTM E2782-10
(Guide)Standard Guide for Measurement Systems Analysis (MSA)
Standard Guide for Measurement Systems Analysis (MSA)
SIGNIFICANCE AND USE
Many types of measurements are made routinely in research organizations, business and industry, and government and academic agencies. Typically, data are generated from experimental effort or as observational studies. From such data, management decisions are made that may have wide-reaching social, economic, and political impact. Data and decision making go hand in hand and that is why the quality of any measurement is importantfor data originate from a measurement process. This guide presents selected concepts and methods useful for describing and understanding the measurement process. This guide is not intended to be a comprehensive survey of this topic.
Any measurement result will be said to originate from a measurement process or system. The measurement process will consist of a number of input variables and general conditions that affect the final value of the measurement. The process variables, hardware and software and their properties, and the human effort required to obtain a measurement constitute the measurement process. A measurement process will have several properties that characterize the effect of the several variables and general conditions on the measurement results. It is the properties of the measurement process that are of primary interest in any such study. The term “measurement systems analysis” or MSA study is used to describe the several methods used to characterize the measurement process.
Note 1—Sample statistics discussed in this guide are as described in Practice E2586; control chart methodologies are as described in Practice E2587.
SCOPE
1.1 This guide presents terminology, concepts, and selected methods and formulas useful for measurement systems analysis (MSA). Measurement systems analysis may be broadly described as a body of theory and methodology that applies to the non-destructive measurement of the physical properties of manufactured objects.
1.2 Units—The system of units for this guide is not specified. Dimensional quantities in the guide are presented only as illustrations of calculation methods and are not binding on products or test methods treated.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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An American National Standard
Designation:E2782–10
Standard Guide for
Measurement Systems Analysis (MSA)
This standard is issued under the fixed designation E2782; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope experimental work under the auspices of a scientific or
engineering group. E177
1.1 This guide presents terminology, concepts, and selected
3.1.2 calibration, n—process of establishing a relationship
methods and formulas useful for measurement systems analy-
between a measurement device and a known standard value(s).
sis (MSA). Measurement systems analysis may be broadly
3.1.3 gage, n—device used as part of the measurement
described as a body of theory and methodology that applies to
process to obtain a measurement result.
the non-destructive measurement of the physical properties of
3.1.4 measurement process, n—process used to assign a
manufactured objects.
number to a property of an object or other physical entity.
1.2 Units—The system of units for this guide is not speci-
3.1.4.1 Discussion—The term “measurement system” is
fied. Dimensional quantities in the guide are presented only as
sometimes used in place of measurement process.
illustrations of calculation methods and are not binding on
3.1.5 measurementresult,n—numberassignedtoaproperty
products or test methods treated.
of an object or other physical entity being measured.
1.3 This standard does not purport to address all of the
3.1.5.1 Discussion—The word “measurement” is used in
safety concerns, if any, associated with its use. It is the
the same sense as measurement result.
responsibility of the user of this standard to establish appro-
3.1.6 measurement system, n—the collection of hardware,
priate safety and health practices and determine the applica-
software, procedures and methods, human effort, environmen-
bility of regulatory limitations prior to use.
tal conditions, associated devices, and the objects that are
2. Referenced Documents measured for the purpose of producing a measurement.
3.1.7 measurement systems analysis (MSA), n—any of a
2.1 ASTM Standards:
number of specialized methods useful for studying a measure-
E177 Practice for Use of the Terms Precision and Bias in
ment system and its properties.
ASTM Test Methods
3.2 Definitions of Terms Specific to This Standard:
E456 Terminology Relating to Quality and Statistics
3.2.1 appraiser, n—the person who uses a gage or measure-
E2586 Practice for Calculating and Using Basic Statistics
ment system.
E2587 Practice for Use of Control Charts in Statistical
3.2.2 discrimination ratio, n—statistical ratio calculated
Process Control
from the statistics from a gage R&R study that measures the
3. Terminology
number of 97 % confidence intervals, constructed from gage
R&R variation, that fit within six standard deviations of true
3.1 Definitions—Unless otherwise noted, terms relating to
object variation.
quality and statistics are defined in Terminology E456.
3.2.3 distinct product categories, n—alternate meaning of
3.1.1 accepted reference value, n—a value that serves as an
the discrimination ratio.
agreed-upon reference for comparison, and which is derive-
3.2.4 gage consistency, n—constancy of repeatability vari-
d.as: (1) a theoretical or established value, based on scientific
ance over a period of time.
principles, (2) an assigned or certified value, based on experi-
3.2.4.1 Discussion—Consistency means that the variation
mental work of some national or international organization, or
within measurements of the same object (or group of objects)
(3) a consensus or certified value, based on collaborative
under the same conditions by the same appraiser behaves in a
state of statistical control as judged, for example, using a
This guide is under the jurisdiction of ASTM Committee E11 on Quality and
control chart. See Practice E2587.
Statistics and is the direct responsibility of Subcommittee E11.20 on Test Method
3.2.5 gage performance curve, n—curve that shows the
Evaluation and Quality Control.
Current edition approved Oct. 1, 2010. Published November 2010. DOI: probability of gage acceptance of an object given its real value
10.1520/E2782-10.
or the probability that an object’s real measure meets a
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
requirement given the measurement of the object.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2782–10
3.2.6 gage R&R, n—combined effect of gage repeatability interest in any such study. The term “measurement systems
and reproducibility. analysis”orMSAstudyisusedtodescribetheseveralmethods
3.2.7 gage resolution, n—degree to which a gage can used to characterize the measurement process.
discriminate between differing objects.
NOTE 1—Sample statistics discussed in this guide are as described in
3.2.7.1 Discussion—The smallest difference between two
Practice E2586; control chart methodologies are as described in Practice
objects that a gage is capable of detecting is referred to as its
E2587.
finiteresolutionproperty.Forexample,alinearscalegraduated
in tenths of an inch is not capable of discriminating between 5. Characteristics of a Measurement System (Process)
objects that differ by less than 0.1 in. (0.25 cm).
5.1 Measurement has been defined as “the assignment of
3.2.8 gage stability, n—absence of a change, drift, or erratic
numbers to material objects to represent the relations existing
behavior in bias over a period of time.
among them with respect to particular properties. The number
3.2.8.1 Discussion—Stability means that repeated measure-
assigned to some particular property serves to represent the
ments of the same object (or average of a set of objects) under
relative amount of this property associated with the object
the same conditions by the same appraiser behave in a state of 3
concerned.” (1)
statistical control as judged for example by using a control
5.2 Ameasurement system may be described as a collection
chart technique. See Practice E2587.
of hardware, software, procedures and methods, human effort,
3.2.9 linearity, n—difference or change in bias throughout
environmental conditions, associated devices, and the objects
theexpectedoperatingrangeofagageormeasurementsystem.
that are measured for the purpose of producing a measurement.
3.2.10 measurement error, n—error incurred in the process
In the practical working of the measurement system, these
of measurement.
factors combine to cause variation among measurements of the
3.2.10.1 Discussion—As used in this guide, measurement
same object that would not be present if the system were
error includes one or both of R&R types of error.
perfect. A measurement system can have varying degrees of
3.2.11 repeatability conditions, n—in a gage R&R study,
each of these factors, and in some cases, one or more factors
conditionsinwhichindependentmeasurementsareobtainedon
may be the dominant contributor to this variation.
identical objects, or a group of objects, by the same operator
5.2.1 A measurement system is like a manufacturing pro-
using the same measurement system within short intervals of
cess for which the product is a supply of numbers called
time.
measurement results. The measurement system uses input
3.2.11.1 Discussion—As used in this guide, repeatability is
factors and a sequence of steps to produce a result. The inputs
often referred to as equipment variation or EV.
are just varying degrees of the several factors described in 5.2
3.2.12 reproducibility conditions, n—in a gage R&R study,
including the objects being measured.The sequence of process
conditions in which independent test results are obtained with
steps are that which would be described in a method or
the same method, on identical test items by different operators.
procedure for producing the measurement. Taken as a whole,
3.2.12.1 Discussion—As used in this guide, reproducibility
the various factors and the process steps work collectively to
is often referred to as appraiser variation or AV. This term is
form the measurement system/process.
also used in a broader sense in Practice E177.
5.3 An important consideration in analyzing any measure-
ment process is its interaction with time. This gives rise to the
4. Significance and Use
properties of stability and consistency. A system that is stable
4.1 Many types of measurements are made routinely in
and consistent is one that is predictable, within limits, over a
research organizations, business and industry, and government
period of time. Such a system has properties that do not
and academic agencies. Typically, data are generated from
deteriorate with time (at least within some set time period) and
experimentaleffortorasobservationalstudies.Fromsuchdata,
is said to be in a state of statistical control. Statistical control,
management decisions are made that may have wide-reaching
stability and consistency, and predictability have the same
social, economic, and political impact. Data and decision
meaning in this sense. Measurement system instability and
making go hand in hand and that is why the quality of any
inconsistency will cause further added overall variation over a
measurement is important—for data originate from a measure-
period of time.
ment process. This guide presents selected concepts and
5.3.1 In general, instability is a common problem in mea-
methods useful for describing and understanding the measure-
surement systems. Mechanical and electrical components may
mentprocess.Thisguideisnotintendedtobeacomprehensive
wear or degrade with time, human effort may exhibit increas-
survey of this topic.
ing fatigue with time, software and procedures may change
4.2 Any measurement result will be said to originate from a
with time, environmental variables will vary with time, and so
measurementprocessorsystem.Themeasurementprocesswill
forth. Thus, measurement system stability is of primary con-
consist of a number of input variables and general conditions
cern in any ongoing measurement effort.
that affect the final value of the measurement. The process
5.4 There are several basic properties of measurement
variables, hardware and software and their properties, and the
systems that are widely recognized among practitioners. These
human effort required to obtain a measurement constitute the
measurement process. A measurement process will have sev-
eral properties that characterize the effect of the several
variables and general conditions on the measurement results. It
The boldface numbers in parentheses refer to the list of references at the end of
isthepropertiesofthemeasurementprocessthatareofprimary this standard.
E2782–10
are repeatability, reproducibility, linearity, bias, stability, con-
sistency, and resolution. In studying one or more of these
properties,thefinalresultofanysuchstudyissomeassessment
of the capability of the measurement system with respect to the
property under investigation. Capability may be cast in several
ways, and this may also be application dependent. One of the
primary objectives in any MSA effort is to assess variation
attributabletothevariousfactorsofthesystem.Allofthebasic
properties assess variation in some form.
5.4.1 Repeatabilityisthevariationthatresultswhenasingle
FIG. 2 Reproducibility Concept
object is repeatedly measured in the same way, by the same
appraiser, under the same conditions (see Fig. 1). The term
5.4.5 Stability is variation in bias with time, usually a drift
“precision” also denotes the same concept, but “repeatability”
or trend, or erratic behavior.
is found more often in measurement applications. The term
5.4.6 Consistencyisthechangeinrepeatabilitywithtime.A
“conditions” is sometimes combined with repeatability to
system is consistent with time when the standard deviation of
denote “repeatability conditions” (see Terminology E456).
the repeatability error remains constant. When a measurement
5.4.1.1 Thephrase“intermediateprecision”isalsoused(for
system is stable and consistent, we say that it is a state of
example, see Practice E177). The user of a measurement
statistical control.
system shall decide what constitutes “repeatability conditions”
5.4.7 The resolution of a measurement system has to do
or “intermediate precision conditions” for the given applica-
with its ability to discriminate between different objects. A
tion. Typically, repeatability conditions for MSA will be as
system with high resolution is one that is sensitive to small
described above.
changesfromobjecttoobject.Inadequateresolutionmayresult
5.4.2 Reproducibility is defined as the variation among
in identical measurements when the same object is measured
average values as determined by several appraisers when
several times under identical conditions. In this scenario, the
measuring the same group of objects using identical measure-
measurement device is not capable of picking up variation as a
ment systems under the same conditions (see Fig. 2). In a
result of repeatability (under the conditions defined). Poor
broader sense, this may be taken as variation in average values
resolution may also result in identical measurements when
of samples, either identical or selected at random from one
differing objects are measured. In this scenario, the objects
homogeneous population, among several laboratories or as
themselves are too close in true magnitude for the system to
measured using several systems.
distinguish among.
5.4.2.1 Reproducibility may include different equipment
5.4.7.1 Resolution plays an important role in measurement
and measurement conditions. This broader interpretation has
in general. We can imagine the output of a process that is in
attached “reproducibility conditions” and shall be defined and
statistical control and follows a normal distribution with mean,
interpreted by the user of a measurement system. (In Practice
µ, and standard deviation, s. Based on the normal distribution,
E177, reproducibility includes interlaboratory variation.)
the natural spread of the process is 6s. Suppose we measure
5.4.3 Bias is the difference between a standard or accepted
objects from this process with a perfect gage except for its
reference value for an object, often called a “master,” and the
finite resolution property. Suppose further that the gage we a
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