My Reading on ASQ CQA HB Part V Part 2

Part VD2
Process capability index.
In process improvement efforts, the process capability index or process capability ratio is a statistical measure
of process capability: the ability of a process to produce output within specification limits. The concept of
process capability only holds meaning for processes that are in a state of statistical control. Process capability
indices measure how much "natural variation" a process experiences relative to its specification limits and
allows different processes to be compared with respect to how well an organization controls them.
If the upper and lower specification limits of the process are USL and LSL, the target process mean is T, the
estimated mean of the process is μ and the estimated variability of the process (expressed as a standard
deviation) is σ, then commonly accepted process capability indices include:
C pk
Adjusted Sigma
level (σ)
Area under the Ф
(σ)
Process yield
0.33 1 0.3085375387 30.85% 691462
0.67 2 0.6914624613 69.15% 308538
1.00 3 0.9331927987 93.32% 66807
1.33 4 0.9937903347 99.38% 6209
1.67 5 0.9997673709 99.9767% 232.6
2.00 6 0.9999966023 99.99966% 3.40
DPMO : defects per million opportunities or (or nonconformities per million opportunities (NPMO)
Process fallout
(in terms of DPMO/PPM)
https://en.wikipedia.org/wiki/Process_capability_index
Charlie Chong/ Fion Zhang