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The calculations performed by TP414 are thoroughly described in "Quality Control and Industrial Statistics" by Acheson J. Duncan, Ph D. The publisher is Richard Irwin, Inc. The book shows the common statistical methodology that underlies both Mil-Std-414 and TP414.
TP414 uses the same mathematics as the Mil-Std-414 "K" method for percent non-conforming. But TP414 goes beyond the capability of Mil-Std-414 in several ways.
One of the most important ways that TP414 goes beyond Mil-Std-414 is that it enables you to design sampling plans based on the mean, both fixed-n and sequential, as described in Duncan.
Mil-Std-414 does not make a good reference standard when sampling for the mean. Rather, refer the the method for the mean in Duncan. Another valuable reference is "Specifications for the Chemical Process Industries" by the ASQC Chemical and Process Industries Division.
TP414 is compatible with both of these sources in its method of calculating OC-Curves.
We try to keep in touch with customers who deal with FDA and other inspections, and can discuss how to justify two-point sampling plans, and their compatibility with national standard plans.
Our Technical Director is currently chairman of an ASQ working group to convert the standards ISO-8422 and IOS-8423 into ASQ/ANSI standards. These standards are for sequential sampling plans for variables and attributes.