np Chart Formulas
The np chart is used to evaluate process stability when counting the number or fraction defective.
The np chart is useful when it's easy to count the number of defective items and the sample size is always the same. Examples might include: the number of defective circuit boards per 100 or errors per each sample of 50 invoices.
Here is the formula used to calculate a np chart.
Conforms with ANSI/ASQC B1, B2, B3 1996
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