np Chart Formulas

QI Macros Can Calculate Them For You!

Draw a np Chart using QI Macros

  1. Select your data.
  2. Select np chart on QI Macros menu.
  3. QI Macros will do the math and draw the graph for you.

Go Deeper

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.

np chart formula

Conforms with ANSI/ASQC B1, B2, B3 1996

NOTE: It is not possible to have negative limits on an np Chart. With that, any calculated value that is below 0 is automatically changed to 0.

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The np Chart is just one of the tools included in QI Macros SPC Software for Excel.

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