Which statement about control charts is false?

Control charts are a fundamental tool in quality control that help monitor the stability of a process over time. They graphically display data points concerning the control limits, which are derived from the process's historical performance. One of the key purposes of control charts is to track variations in process outputs and to signal when a process may be going out of control due to special cause variation.

When analyzing option C, it’s important to note that values above the upper control limit are indicative of an out-of-control condition rather than excellent quality. In fact, they suggest that the process may be producing defective items or experiencing issues that need immediate attention. Therefore, stating that such values indicate excellent quality is fundamentally incorrect.

The other options accurately describe the functions and characteristics of control charts. They graphically present data, allowing for straightforward visual analysis of a process's performance. They indeed facilitate the quick comparison of new data with historical performance to detect any deviations. Additionally, control charts are beneficial in identifying trends, signaling when adjustments might be needed to maintain quality in production.