Hach ORBISPHERE 51 Series User Manual page 50

CPm process repeatability
Capability index that takes into account variation between the process average and the target. If the
process average and the target are the same value, Cpm will be the same as Cpk. If the average
drifts from the target, Cpm will be less than Cpk.
Skewness
negative
positive
Figure 34 Skewness
Kurtosis
Figure 35 Kurtosis
An asymmetric frequency distribution is skewed to the left if the lower tail
is longer than the upper tail, and skewed to the right if the upper tail is
longer than the lower tail. Distributions of positive-valued random
variables values are often skewed right.
Kurtosis is a parameter that describes the shape of a random variable's
probability distribution.
The graphs on the left illustrate the notion of kurtosis. The lower curve
has higher kurtosis than the upper curve. It is more peaked at the center,
and it has fatter tails
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