Table of Contents
SPC Quick Check Guide
Learn how to analyze your process data in 6 simple steps. Get control charts, histograms, and capability indices in minutes.
Start SPC Quick CheckWhat Is SPC Quick Check?
Statistical Process Control (SPC) helps you determine if your manufacturing process is stable and predictable. The SPC Quick Check tool takes your measurement data and generates an XmR control chart, a histogram, and capability indices (Cp and Cpk) so you can see at a glance whether your process is in control and meeting specifications.
When Should I Use This Tool?
- After collecting measurements from a production run to verify process stability
- During incoming inspection to check if a supplier's parts are within tolerance
- When setting up a new machine or process to establish baseline performance
- As part of a PPAP or APQP submission that requires control charts and capability studies
Before You Start
Have the following information ready before starting your analysis:
- At least 10 measurement values (20 or more recommended for reliable results)
- Upper and/or Lower specification limits from your drawing or specification (optional, needed for Cp/Cpk)
- A descriptive title for your analysis (e.g., part number, feature name, operation)
1 Setup Your Analysis
Start by giving your analysis a name and optionally entering your specification limits. These limits come from your part drawing or quality specification.
- Analysis Title (required)
- A descriptive name that helps you identify this analysis later. Example: "Part #12345 - OD Diameter - CNC Mill #3"
- Upper Spec Limit - USL (optional)
- The maximum acceptable value from your drawing or spec. Example: 25.10 mm
- Lower Spec Limit - LSL (optional)
- The minimum acceptable value from your drawing or spec. Example: 24.90 mm
- Notes (optional)
- Add context like machine name, operator, material batch, or measurement conditions.
Click to view screenshot
2 Enter Your Data
Paste or type your measurement data. You can enter one value per line, or use one of the structured formats if you want to include timestamps or tags with each measurement.
Data Format Options
- Value Only
- One number per line. The simplest format -- just paste your measurements. Example: 25.01, 25.03, 24.98...
- Date + Value
- A date/time followed by a value, separated by a comma or tab. Useful when you want to see measurements over time.
- Tag + Value
- A label (like a sample ID or operator name) followed by a value. Helpful for tracing each measurement.
Choose the data format that matches how your data is organized
Click to view screenshot
3 Review Your Control Chart
The XmR (Individuals and Moving Range) chart shows each measurement plotted in order. Three reference lines help you evaluate stability:
- Center Line (CL)
- The average of all your measurements. Your process is centered around this value.
- Upper Control Limit (UCL)
- Calculated at 3 sigma above the center line. Points above this line may indicate a special cause of variation.
- Lower Control Limit (LCL)
- Calculated at 3 sigma below the center line. Points below this line may indicate a special cause of variation.
Click to view screenshot
4 View the Histogram
The histogram shows how your measurements are distributed. A bell-shaped (normal) distribution centered between the spec limits indicates a healthy process. If you entered specification limits, they appear as vertical lines so you can see how much of your data falls within tolerance.
Click to view screenshot
5 Check Process Capability
If you entered specification limits in Step 1, this step calculates two key capability indices that tell you how well your process fits within the tolerance band:
- Cp
- Process Capability. Compares the width of the tolerance band to the width of your process variation. A Cp of 1.33 or higher is generally considered capable. This metric does not account for centering.
- Cpk
- Process Capability Index. Like Cp, but also accounts for how well the process is centered within the tolerance. A Cpk of 1.33 or higher means your process is both capable and centered. If Cpk is much lower than Cp, your process is off-center.
Click to view screenshot
6 Save or Download Your Report
Your complete SPC report includes the control chart, histogram, capability indices, and all the details you entered. From here you can save it to your dashboard, download it as a PDF, or share it with a colleague.
Click to view screenshot
Understanding Your Results
A process that is "in control" shows only common cause variation -- all points fall within the control limits with no obvious patterns. Look for points outside the control limits, runs of 7+ points on one side of the center line, or trending patterns. Any of these signals may indicate a special cause that should be investigated.
Common out-of-control signals: points beyond limits, runs, and trends
Tips & Best Practices
- Collect at least 20-25 data points for reliable control limits and capability estimates.
- Measure parts in the order they were produced. The control chart relies on data sequence to detect trends.
- Do not mix data from different machines, operators, or setups in one analysis unless that is what you intend to study.
- Run this tool after every shift change or setup to catch process drift early.
- If your process is out of control, use the Fishbone Diagram or 5 Whys RCA tool to investigate the root cause before adjusting.