367. U-Chart

Defects per unit (variable unit size)

Where:

• ${𝑐}_{𝑖}$: number of defects in sample $𝑖$
• ${𝑛}_{𝑖}$: sample size of group $𝑖$
• ${𝑢}_{𝑖}$: defects per unit

• $\overline{𝑢}$: