Struct NPChart 

pub struct NPChart { /* private fields */ }

Count of nonconforming items (NP) chart.

Monitors the count of defective items in samples of constant size. Simpler than the P chart when sample sizes are uniform.

Formulas

• CL = n * p-bar
• UCL = n * p-bar + 3 * sqrt(n * p-bar * (1 - p-bar))
• LCL = max(0, n * p-bar - 3 * sqrt(n * p-bar * (1 - p-bar)))

Reference

Montgomery, D.C. (2019). Introduction to Statistical Quality Control, 8th ed., Chapter 7, Section 7.3.

Implementations

impl NPChart

pub fn new(sample_size: u64) -> Result<Self, ControlChartError>

Create a new NP chart with a constant sample size.

Errors

Returns ControlChartError::ZeroSampleSize when sample_size == 0. The size usually comes from data, so this is an ordinary outcome rather than a contract violation – and a boundary that cannot unwind, such as the WebAssembly entry points, needs it as a value.

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

Add a defective count for one subgroup.

Errors

ControlChartError::DefectivesExceedSampleSize if defectives exceeds the chart’s sample size. The chart is left unchanged.

pub fn control_limits(&self) -> Option<(f64, f64, f64)>

Get the control limits as (ucl, cl, lcl), 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.