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NP Chart Maker

You can easily create a NP Chart online here! Simply copy your data into the table and select the measurements.

NP Chart Maker

Create an NP Chart online

In Statistical Process Control (SPC), an NP Chart is a type of control chart used to monitor the number of defective items or nonconformities in a process when the sample size remains constant. It is an extension of the P Chart and is particularly useful when the data being collected consists of discrete counts of defective items or nonconformities and the sample size for each observation is fixed.

How It Works:

  • Data Collection: The NP Chart collects data on the number of defective items or nonconformities observed in each sample, where the sample size remains constant.
  • Plotting the Chart: On the NP Chart, the counts of defective items or nonconformities are plotted over time or by sample number on the horizontal axis.
  • Center Line and Control Limits: A center line is drawn on the chart to represent the average or mean number of defective items across all samples. Upper and lower control limits are also calculated based on the variability of the defect counts and are typically set at a certain number of standard deviations from the center line.
  • Interpreting the Chart: Similar to other control charts, when the counts of defective items fall within the control limits and show random variation around the center line, it indicates that the process is stable and under statistical control. Any data points falling outside the control limits or showing non-random patterns suggest that the process may be experiencing special causes of variation, necessitating further investigation and corrective action.

The NP Chart is commonly used in quality control and process improvement efforts, especially in industries where the sample size for each observation remains constant. By monitoring the number of defective items per sample over time, organizations can identify trends, patterns, and potential issues in their processes and take appropriate actions to maintain quality standards and improve overall process performance.

Cite DATAtab: DATAtab Team (2025). DATAtab: Online Statistics Calculator. DATAtab e.U. Graz, Austria. URL https://datatab.net

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