U Control Chart (Defects per Unit) Online
Online u chart: monitor defects per unit when sample sizes vary, automatically calculating ū and variable control limits with automatic detection of the eight out-of-control rules.
Why are the u chart control limits not straight lines?
The u chart control limits are ū ± 3√(ū/nᵢ), which depend on each sample size nᵢ; the larger the sample, the narrower the limits.