Calibration and Documentation 371

accuracy

The difference between a measurement reading and the true value of that measurement. Accurate measurements contain less error.

American Association for Laboratory Accreditation

A2LA. An independent society in the United States that accredits laboratories using internationally-accepted standards. A2LA standards are more strict than ISO 9000 and 17025.

anvil

A fixed jaw against which an object to be measured is placed. On a micrometer, the anvil is an immobile block from which the measurement is taken.

audit

An examination of a company's activities or products to determine if a company is in compliance with standards. Audits must be completed both internally and externally.

calibration

The comparison and adjustment of a device with unknown accuracy to a device with a known, accurate standard. Calibration eliminates any variation in the device being checked.

calibration laboratory

A controlled test environment where higher-level calibration is performed. Calibration laboratory results should be traced back to international standards.

calibration records

A document displayed with a measuring instrument that contains information about its calibration. Calibration records help maintain accuracy and traceability.

calibration report

A document that contains information about a particular calibration procedure. Calibration reports maintain traceability.

calibration technician

An employee that maintains, tests, and repairs gages and other testing equipment. A calibration technician is responsible for making sure that all equipment is calibrated and that all lab documentation and processes are organized and up-to-date.

caliper

A measuring instrument with a pair of jaws on one end and a long beam containing a marked scale of unit divisions. The jaws can measure both internal and external features.

cataloged number

A unique number that distinguishes one measuring instrument from another. Cataloged numbers are used in documentation and must be included on a measuring instrument's calibration label.

coordinate measuring machines

CMM. A sophisticated measuring instrument with a flat polished table and a suspended probe that measures parts in three-dimensional space. CMMs can measure using either contact or noncontact methods.

correction factors

The amount of deviation in a measurement that is accounted for in the calibration process. The correction factor can be added to the measured value, or the measuring instrument can be adjusted.

documentation

The process in which records and information about calibration and lab practices are kept for reference and traceability purposes. Both ISO 9000 and ISO 17025 require proper documentation for certification and accreditation.

error

The difference between a measured value and its correct value. Errors should be eliminated from the measuring process.

external audits

An audit completed by an outside agency. External audits are completed yearly to make sure that a company follows all regulations for certification.

eyepiece

The rubber cylinder of a refractometer located at the end opposite the cover plate. The eyepiece is used to look into the refractometer to view the Brix scale percentage reading.

gage block

A hardened steel block manufactured with highly accurate dimensions that is used to check the accuracy of inspection devices. Gage blocks are available in a set of standardized lengths.

gage tracking system

A method of document control in which all documentation required to maintain traceability for each gage is reviewed, organized, and up-to-date. Most labs achieve a gage tracking system through inexpensive software.

gages

A device that physically inspects part features. Gages have an established standard size.

gaging repeatability and reproducibility

R&R. A study that discovers the total amount of variation in a measurement. By combining the variation of the instrument with the variation of the operator, R&R can calculate how precise a measurement can be.

hardness testing

A test that determines a material's ability to resist penetration. Hardness testing equipment is sensitive and should be stored in an area free of humidity and abrupt temperature changes.

inspection

The examination of a part during or after its creation to confirm that it adheres to specifications. During inspection, defects may be identified and corrected.

internal audits

An audit completed by the company itself to check that it continues to meet required regulations. Internal audits are completed in preparation for external audits and should be conducted in a similar manner.

ISO 17025:2005

The most recent standards for calibration laboratory accreditation published by the International Organization for Standardization. ISO 17025:2005 follows the regulations in place for ISO 9000 but adds requirements to ensure reliability of product accuracy.

ISO 9000

A standard published by the International Organization for Standardization that lists requirements for the creation and implementation of an effective quality management system. ISO 9000 helps ensure that processes and activities satisfy customer needs.

mastering

A quick check of a measuring device against a known standard reference to determine if the device is reading the measurement correctly. Mastering is often performed using a gage block.

measurement standard

A recognized true value. Calibration must compare measurement values to a known standard.

metrology

The science of measurement. Metrology strives for accuracy, precision, and repeatability.

micrometers

A U-shaped measuring instrument with a threaded spindle that slowly advances toward a small anvil. Unlike most measuring instruments, micrometers can often be calibrated in-house.

precision

The degree to which an instrument will repeat the same measurement over a period of time. Precision is also called repeatability, as it will show the same results under unchanged conditions.

quality management system

QMS. The objectives and processes of a company designed to focus the company toward quality and customer satisfaction. The QMS consists of written documents that address standards like ISO 9000 standard ISO 17025.

quality manual

A document that describes a company's overall plan for proper quality management and documentation control. The quality manual should contain a quality policy statement and a list of standard operating procedures.

quality policy statement

A statement contained in a company's quality manual. The quality policy statement should state the company's commitment to quality in a nonspecific manner.

repeatability

The ability of an object to deliver accurate and dependable results over a long period of time. Repeatability describes the variation of a measuring instrument and, when combined with the variation of the operator, can be used to calculate the precision in a measurement.

reproducibility

The difference in the average of groups of repeated measurements made by different operators. Reproducibility describes the variation of the operator and, when combined with the variation of the measuring instrument, can be used to calculate the precision in a measurement.

spindle

The rotating component of a tool. On a micrometer, the spindle advances toward the anvil to make contact with the part.

standard operating procedures

SOP. A document describing an organization's routine processes. An SOP contains a moderate amount of detail about the techniques and equipment used to create a set of work instructions for employees to follow.

tolerances

The total amount a specific dimension is permitted to vary. The object will still meet specifications if it remains within its tolerance.

traceability

The ability to verify the history, application, or location of an item using documentation. For an instrument's calibration to be traceable, it must follow the hierarchy of standards through to the national or international standard.

uncertainty

The measurement range in which the true value of a measurement is expected to lie. Uncertainty is the amount of variation that is acceptable in a measurement.

working standard

A measurement standard used to calibrate or master measuring instruments. Gage blocks are often used as a working standard.

zero out

Changing a digital reading to measure zero. Zero out a digital micrometer that does not read zero when the spindle and anvil make firm contact.

zero reading

A measurement of zero on an inspection device. A zero reading on a micrometer should occur when the spindle and anvil contact each other.

zero-check

A method for ensuring that an inspection instrument has an accurate zero reading. To zero-check a micrometer, maintain firm contact between the spindle and anvil when the micrometer measures zero in either inches or millimeters.