Displays the measured concentration or value of the control material. Historical Context

Two consecutive points differ by more than 4 SD (e.g., one is at +2 SD and the next is at -2 SD), indicating high variability or random error.

Imagine you run a glucose QC sample daily. Your mean = 100 mg/dL, SD = 5 mg/dL.

In the world of clinical lab testing, accuracy is non-negotiable. A single erroneous result can lead to a misdiagnosis, unnecessary treatment, or a missed critical condition. That’s where the becomes indispensable. Think of it as a trend-tracking “vitals monitor” for your testing process —it helps you see at a glance whether your instruments and methods are stable and reliable.

The (often abbreviated as L-J chart) is a fundamental tool used in laboratory medicine and quality control. While it might look like a simple line graph, its "interesting feature" lies in how it visualizes stability over time .