Column: Measure for Measure: Meeting Specifications


Stein, Philip   (2002, Philip Stein and ASQ)  

Quality Progress    Vol. 35    No. 3
QICID: 15366    March 2002    pp. 81-82
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Article Abstract

Particular specifications may be critical to the customer's uses, but the resolution given is less than the manufacturer's instruments provide, as when the specification reads 3.5 but the instruments can measure 3.4999. To what extent can one round?

Again, while an agreement may have been reached on the rounding issue, an instrument may be off and may measure incorrectly in one direction or the other. Finally, even the precise time of an expiration may be in question: does a particular certification expire at the beginning of the stated day or at its end?

Company policy must be set to deal with these things so that a locally consistent rule is kept, because there is no standard answer. ISO 14253-1 states that any time a measurement is close to a boundary, it must be rated as "uncertain," but this does not help customers. The final decision on how to deal with boundary issues must rest with the customer. The resulting interpretation is called a "guardband."


Measurement and control,Uncertainty,Metrology

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