Six Sigma Black Belt Practice Exam 2025 – Complete Prep Resource

The u control chart is specifically designed for monitoring the count of defects per unit when dealing with variable sample sizes. This chart is particularly suited for situations where the number of units in each sample can differ, making it useful in industries where products or batches may come in various quantities.

The u chart calculates the average number of defects per unit, or the defect rate, which provides insights into the process capability and consistency over time. By utilizing this control chart, an organization can effectively identify variations in the defect rate, helping to highlight improvement opportunities and maintain quality standards.

In comparison, the np chart is used for monitoring the number of defective items in fixed sample sizes, while the c chart focuses specifically on count defects in a constant area or sample size. The p chart monitors the proportion of defective items, which requires constant sample sizes as well to provide valid results. Therefore, the u chart is the most appropriate choice when dealing with varying sample sizes and monitoring defect counts.