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The reference environmental conditions listed below are gradually being adopted internationally.
Although it is possible for standards laboratories to work under other environmental conditions and to correct their measurement results so as to represent the calibration information at the reference conditions, considerable extra work and meticulous data processing is necessary to ensure that correct results are reported.
Measurement standards used for Type III services are robust and are generally not subject to large drift or change within the laboratory’s scope of measurement.
NOTES: A material measure, measuring instrument, reference material, or measuring system intended to define, realize, conserve, or reproduce a unit or one or more values of a quantity to serve as a property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties.
Type I: A service that is intended primarily for the calibration of measurement standards.
The laboratory instead assures the quality of the measurement results through such other quality control techniques as interlaboratory comparison, replication, retesting, and correlation with other measurement characteristics.
Although the set points of variables, such as temperature, are important, a more important aspect is the stability of the environment during the time taken to make a calibration measurement.
Limits on the rates of change of the environmental conditions are important to all laboratories, and should be established and maintained in all calibration laboratories.
The overall operation of a standards laboratory or of a test equipment calibration laboratory is simplified when the same reference environmental conditions are maintained in calibration laboratories and in external client laboratories.
This decreases the probability of errors when writing or implementing reports.
The requirement for temperature stability applies only to the space occupied by the standards and the comparison or measuring equipment, although the larger the volume in which the conditions are stable the greater would be the confidence in the measurement results.