Tools › Quality › Control › SPC and Capability › Example
Montgomery Example 7.1: p chart of nonconforming orange-juice cans
| Tool | SPC and Capability |
| Source | Montgomery, D. C. (2013). Introduction to Statistical Quality Control, 7th ed. Wiley, Hoboken, NJ. Example 7.1, Table 7.1. |
| Level | Undergraduate |
Problem
Thirty samples of 50 cardboard cans each were inspected for leaks at half-hour intervals; 347 of the 1,500 cans were nonconforming. Compute the trial centre line and three-sigma limits of the fraction-nonconforming chart.
Inputs to Enter
- Chart type p (each line = defectives, sample size)
- 30 lines from Table 7.1, each 'd_i 50', with Σd_i = 347
Answers
- p̄ = 347/1500 = 0.2313
- UCL = p̄ + 3 √(p̄(1 − p̄)/50) = 0.4102
- LCL = 0.0524
- np chart on the same data: centre line n p̄ = 11.567
Notes
The limits depend only on the totals, so the test script rebuilds them from 347 defectives in 30 samples of 50; to draw the chart itself paste the thirty per-sample counts of Table 7.1. Not the default case: select the p chart and replace the default data.