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4.3. Validation in LTA-STC charts
The global validity of a
QC vector results from
two simultaneous
criteria
1- The global univariate
validity as explained
above
2- No capability alarm:
The bottom row of the
grid shows the lowest
Cpk value observed
among the control
levels. The number of
the relevant level is
displayed between
brackets (2 on the
picture). An exception
is raised if this lowest
Cpk is less than 1. See
section 7.3 to enhance
the default threshold 1.
1
2
Acceptance
interval
: Icons that show whether the capability of the
analytical process is high enough to meet the
specifications. This icon is red if the lowest Cpk
value among the QC levels is less than the threshold
entered in the Analytes dialog (default = 1).
3- The control interval of a LTA-STC chart is based
on the latest known EWMA and three short-term
SD’s.
The Cpk value taken into account for the acceptance
test is the Cpk value that would be observed,
assuming that the QC point under validation is
accepted.
Latest known
EWMA
3
Control
interval
QC point under
validation
21