Struct UChart 

pub struct UChart { /* private fields */ }

Defects per unit (U) chart.

Monitors the defect rate when the area of opportunity (inspection size) varies between subgroups. Control limits are computed individually for each subgroup based on its inspection size.

Formulas

• CL = u-bar = total_defects / total_units
• UCL_i = u-bar + 3 * sqrt(u-bar / n_i)
• LCL_i = max(0, u-bar - 3 * sqrt(u-bar / n_i))

A known u-bar from a Phase I study is given with UChart::with_center; see PChart for why it is not re-estimated from later samples.

Reference

Montgomery, D.C. (2019). Introduction to Statistical Quality Control, 8th ed., Chapter 7, Section 7.4.

Implementations

impl UChart

pub fn new() -> Self

Create a new U chart that estimates u-bar from its samples (Phase I).

pub fn with_center(u_bar: f64) -> Result<Self, ControlChartError>

Create a U chart whose centre line is a known u-bar (Phase II).

Errors

ControlChartError::InvalidStandard unless u_bar is finite and positive.

pub fn add_sample( &mut self, defects: u64, units_inspected: f64, ) -> Result<(), ControlChartError>

Add a sample with the number of defects and the number of units inspected.

The units_inspected can be fractional (e.g., area or length).

Errors

ControlChartError::NonPositiveUnits if units_inspected is not a positive, finite number. The chart is left unchanged.

pub fn u_bar(&self) -> Option<f64>

The centre line in use — the known u-bar for a chart built with_center, otherwise the estimate — or None if no data.

pub fn points(&self) -> &[AttributeChartPoint]

Get all chart points.

pub fn is_in_control(&self) -> bool

Check if the process is in statistical control.

Trait Implementations

impl Default for UChart

fn default() -> Self

Returns the “default value” for a type.