6
Terms and Definitions
Accuracy:
Accuracy is the closeness of agreement between the average of a
large number of experimental measurements of a characteristic and the
master value of that characteristic. (See Precision)
Bias:
Bias is the difference between the average
value of all the measurements and the master
value.
Bias is the numerical value used to measure
accuracy.
Capability:
Capability is a measure of a process’s ability to consistently produce a
result that meets the specification
requirements.
Capability can be measured by such indices as
C
p
and
C
pk
.
The
C
pk
of a process improves as the process
average moves towards the target. This can
also be related to the Taguchi Loss Function which is a minimum when
the process average equals the target.
Bias
Reference
Value
Observed
Average
Value
Figure 1. Bias
Process
Variation
Taguchi
Loss
Function
Figure 2. Capability
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