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Named and Custom Control Rule Sets 325
The rules are described as they appear in the literature. In many cases, a given rule actually
specifies two test conditions; the first being a value N out of M above a plus sigma control limit,
and the second being a value N out of M below a minus sigma control limit. Examples of this are
rules #1, #2 and #3 for WECO and Nelson rules. In other cases, similar rules only contain one
test case; N out of M above (or below) a given sigma control limit. Example of this are the Juran
rules #2..#5, Hughes Rules #2..#9, Gitlow Rules #2..#5, and Duncan Rules #2..#5.
While the list of named rules below follow what is presented in the literature, the actual rule
numbering should be ignored. That is because in the software we implement all rules as simple
single condition rules. The first rule in all of the named rule sets is implemented as two rules; a
single point greater than 3-sigma; and a single point less than -3-sigma. And WECO and Nelson
rules #2 and #3 are implemented as four rules; two N out of M greater than x-sigma condition
limits, and two N out of M less than x-sigma condition limits. A complete cross reference to the
named rules listed below, and our own rule number system is found in Table 1. This is important,
because when you try to access a particular named rule within the software, you must use our
rule number system.
Nelson Rules
The Nelson rules are almost identical to the combination of the WECO Runtime and Supplemental
Rules. The only difference is in Rule #4.
4. Nine out of the last nine points plot on the same side of the center line, or target value.
AIAG Rules
1.
2.
3.
4.
One of one point is outside of 3-sigma control limit
Seven out of seven are above or below center line
Seven points in a row increasing
Seven points in a row decreasing
Juran Rules
1.
2.
3.
4.
5.
6.
7.
8.
9.
One of one point is outside of +- 3-sigma control limit
Two of three points above 2-sigma control limit
Two of three points below -2-sigma control limit
Four of five points is above 1-sigma control limit
Four of five points is below -1-sigma control limit
Six points in a row increasing
Six points in a row decreasing
Nine out of nine are above or below center line
Eight points in a row on both sides of center line, none in zone C