For SPC practice beginner, you can use a simple free SPC software which is an Excel Add-In for learning both variable and attribute control charts. To download the free SPC software, please click the link below.

## Free Excel Add-In for Statistical Process Control Charts

The SPC Excel Add-In (SPCCharts.1.4.1.xla) was originally developed by Samuel E. Buttrey and published on Journal of Statistical Software[1] website. However the original software contains two errors[2] which have been fixed in the revision copy (SPCCharts.1.4.1-R1.xla) provided in the download link given above.

Please visit the respective web page of Journal of Statistical Software for instructions on how to install and use the SPC Excel Add-In. There are 4 items listed on the web page:-

- Application Note (pdf) describes how to install and use the SPC Excel Add-In.
- SPCCharts.1.4.1.xla: Original Excel add-in for statistical process control charts (zipped)
- v30i13.xls: Excel spreadsheet with sample data
- v30i13.zip: VBA source code

You only need to download Item 1 & 3.

### Notes on Using X-Bar R Variable Control Chart

Please take note that there are two phases of a Control Chart

1. The **initial study phase** where data from a STABLE[3] process are used to determine control limits. To use the software in this phase, please leave mu & sigma blank in the software.

2. The **operation phase** where control limits determined in initial study phase are used to monitor whether the process has become out-of-control due to either shift in process mean (mu) or increase/decrease in process variability (sigma) or both. To use the software in this phase, please key in mu & sigma calculated using X-Bar-Bar (centre line of X-Bar chart ) and R-Bar (centre line of R chart ) determined in step 1 where:

mu = X-Bar-Bar

sigma = R-Bar/d2 (For subgroups of 5, *d*2 is 2.326. Refer d2 constant table for other subgroup size)

In general, setting operation control limits is an iterative process. Based on the outcome in operation phase, the control limits will need to be reviewed to see whether it reflects the process actual control limits. The initial control limits established might be too tight, resulting in many out-of-control incidents shown on charts although there are nothing special happen to the process.

Western Electric rules check is not supported on variable control charts for this software..

(Similar notes applies for X-Bar S charts)

**Installation Issues**

You may encounter the following issue when installing the free SPC software Excel Add-In:

### Macros are Disabled because Security Level is High

If you get an error message as shown below:

You can resolve it by changing the Macro security level from Low to Medium\High.

(The screenshot shown is from Ms Excel 2002, please use google to find how to do it for other version of Ms Excel)

**Notes**

[1] Journal of Statistical Software is published by the American Statistical Association.

[2] The two errors are:

- “Error – Can’t find project of library” was shown during installation due to “Missing: Ref Edit Control”.
- “Too many comma in parameter box” when clicking ‘Run’ button in control chart setup form with both mu & sigma specified.

[3] A STABLE process is an in-control process that show variation due to common causes only. The process data itself can be used to judge if the process is stable. A quick check can be performed visually first on R (or S) chart to see if it is in-control i.e the the data doesn’t show outlier(s) nor special pattern(s) such as trend etc. Once the R (or S) is confirmed to be in-control, only then look at X-Bar chart for similar checking.