u Chart Formulas

u charts determine stability of "counted" data (e.g., errors per bill, dents in a car door, etc.) when there can be more than one defect per unit and the sample size varies.

Here is the formula used to calculate a u chart.

u chart formula

cᵢ = number of nonconformities
nᵢ = sample size

Conforms with ANSI/ASQC B1, B2, B3 1996

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


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