User's Manual Part 3

MEGAM.O.L.E.® Help System Guide ♦366♦
Cp ≥ 1.33: Data tightly distributed.
Cpk ≥ 1.33: Data well inside spec limits.
Cp = 1.00: Data fills entire spec range.
Cpk = 1.00: Data fills entire spec range.
Cp > 1.00: Data tightly distributed. If it
were centered between the spec limits,
no data would lie beyond those limits.
Cpk < 1.00: Some data is outside the
spec limits.
Cp < 1.00: Data not tightly distributed. If
it were centered between the spec limits,
some data would still lie outside those
limits.
Cpk < 1.00: Some data is outside the
spec limits.
The equations used to calculate the index values are as follows:
.).(*6 DevSt d
LSLUSL
Cp
−
=
.).(*3 DevStd
xUSL
Cpk
−
=
O
R
.).(*3 DevStd
LS Lx
Cpk
−
=
, whichever is less
As can be interpreted from the above equations, Cp gives an indication of how narrow
the data distribution is relative to the width of the specification limits. Essentially, it