SPC Histogram

Visualize your process data distributions with built-in Statistical Process Control — right inside Grafana. SPC Histogram turns your time series data into interactive histograms with automatic control limits, bell curves, capability indices, and a detailed statistics table.

Why SPC Histogram?

Histograms are a fundamental tool for understanding process data. When combined with Statistical Process Control, they answer the key questions about your process:

• Control limits — automatically calculated LCL/UCL lines show whether variation is within expected bounds
• Capability indices — Cp, Cpk, Pp, and Ppk tell you whether your process fits within specification limits
• Bell curves — Gaussian curves fitted using the Levenberg-Marquardt algorithm reveal how closely your data follows a normal distribution
• Statistics at a glance — a built-in table displays n, Mean, Std Dev, Min, Max, and more for every series

Built for Grafana

SPC Histogram is built using Grafana's native visualization components. This means it inherits the look, feel, and behavior you already know:

• Native theming — automatically adapts to light and dark mode
• Standard panel options — legend placement, tooltip behavior, and field overrides work just like any other Grafana panel
• Resizable statistics table — drag the splitter to balance chart and table space, just like Grafana's built-in panels
• Works with any data source — use it with SQL databases, Prometheus, InfluxDB, CSV files, or any other Grafana data source

Features

Feature	Description
Control charts	XmR, Xbar-R, and Xbar-S chart types with automatic LCL/UCL calculation
Bell curves	Gaussian (Levenberg-Marquardt fit) and histogram curve overlays
Statistics table	n, Mean, Std Dev, Min, Max, LCL, UCL, Cp, Cpk, Pp, Ppk per series
Custom control lines	Static values or dynamic values pulled from a separate query
Specification limits	LSL/USL with automatic capability index calculation
Multiple series	Compare distributions side by side or combine into one histogram
Aggregation	Mean, Range, Standard Deviation, and Moving Range modes
Export to CSV	Export statistics, control lines, and histogram buckets to CSV
Interactive tooltips	Bucket counts, control line values, and Gaussian curve values on hover
Resizable layout	Drag the splitter between chart and statistics table

Use Cases

• Manufacturing quality — monitor dimensional tolerances with control limits and capability indices
• Process engineering — track measurement stability and detect shifts in process centering
• Laboratory testing — analyze instrument measurement distributions and repeatability
• Supply chain — monitor incoming material quality against specification limits
• Pharmaceutical — validate process capability for batch manufacturing (Cp/Cpk)

Requirements

• Grafana 11 or later

Getting Started

1. Install the plugin from the Grafana Plugin Catalog
2. Add a new panel and select SPC Histogram as the visualization
3. Connect a data source with time series data
4. Choose a Chart Type (XmR, Xbar-R, or Xbar-S) to enable automatic control limits
5. Add Control Lines for specification limits (LSL/USL) to see capability indices
6. Add a Bell Curve to visualize the distribution fit

Panel Options

Histogram

Option	Description	Default
Bucket count	Approximate number of histogram bars	30
Bucket size	Fixed width for each bucket (overrides bucket count)	Auto
Bucket offset	Shifts bucket boundaries by a fixed amount	0
Combine series	Merge all series into a single histogram	Off
Feature Queries	Select queries excluded from histogram calculations	None

SPC

Option	Description	Default
Chart type	none, X chart (XmR), mR chart (XmR), X chart (Xbar-R), R chart (Xbar-R), X chart (Xbar-S), S chart (Xbar-S)	none
Subgroup size	Number of measurements per subgroup	1
Aggregation type	None, Moving range, Mean, Range, Standard Deviation. Only available when chart type is "none".	None
Control lines	LCL, UCL, Mean, Min, Max, Range, LSL, USL, Gaussian Peak, Custom, Nominal	None

Curve

Option	Description	Default
Add a Bell Curve	Gaussian or Histogram curve with configurable series, line width, and color	None

Statistics Table

Option	Description	Default
Show statistics table	Display the statistics table below the histogram	Off
Visible columns	n, Mean, Std Dev, Min, Max, LCL, UCL, Cp, Cpk, Pp, Ppk	All

Bar Appearance

Option	Description	Default
Fill opacity	Bar fill opacity (0–100%)	80%
Line width	Bar border width (0–10)	1
Gradient mode	None, Opacity, or Hue	None

Documentation

For detailed documentation, configuration guides, and examples, see the full documentation.

Part of the KensoBI SPC Suite

SPC Histogram is part of a growing family of Statistical Process Control plugins for Grafana by Kenso Software:

SPC Chart Panel — Control charts for monitoring process stability over time. Supports Xbar-R, Xbar-S, and XmR charts with automatic calculation of control limits. If you're tracking whether a process is staying in control, this is your starting point.

SPC Pareto Panel — Pareto charts for identifying the most significant factors contributing to defects or issues. Automatic sorting, cumulative percentage lines, and 80/20 threshold analysis help you focus improvement efforts where they matter most.

SPC CAD Panel — Brings 3D geometry into the picture, letting you bind the data from control charts and histograms to physical features on your parts.

License

This software is distributed under the AGPL-3.0-only license — see LICENSE for details.

Support

If you have any questions or feedback, you can:

• Ask a question on the KensoBI Discord channel.
• GitHub Issues: https://github.com/KensoBI/spc-histogram/issues