Paste your process data and instantly see UCL, CL, and LCL — with a live control chart that flags out-of-control points and Western Electric rule violations.
Paste numeric values separated by commas, spaces, or new lines. Minimum 5 data points required.
Choose your chart type, paste your data, and press Calculate to see control limits and a live chart.
UCL and LCL are calculated from the data itself — they represent natural process variation (±3σ). A point outside the limits signals an unusual event, not necessarily a defect. Spec limits are set by the customer; control limits are set by the process.
Use I-MR when you measure one item at a time or data is collected infrequently — one reading per time period. Use X̄-R when you sample groups of 2–10 items at regular intervals and want to detect both mean shifts and variation changes.
Beyond single out-of-control points, Western Electric rules flag non-random patterns: 8 consecutive points on one side of the centre line, 6 points in a trend, or 2 of 3 points in the outer third of the chart — all indicate process changes worth investigating.