Two Wrongs

Browser-Based XmR Charts

Browser-Based XmR Charts

When I started using control charts more seriously, I wrote very simple JavaScript code to create them on the go. As you may guess, it computes the limits from the “baseline” part of the url and adds in the “values” after that.1 There are a few more options you can plug into the url but there’s no documentation so have fun reading 150 lines of JavaScript!

This is not really fit for reporting or consumption by others, but it’s been an invaluable tool for personal use.

Now! Commoncog just announced their version of this idea, which is obviously still in development2 Missing some important features, like non-date abscissae. but seems promising and I don’t think it’s very far until I can start using that instead of my JavaScript.

The reason I still want to bring attention to it now is that the introductory text on their front page is great. Here I have picked out some of the most important parts, but if you have ever wondered why spc matters, start with reading their full introduction.

If you look at lots of numbers in your business, you might know the feeling. Sometimes your numbers go up, and sometimes they go down. Can you say, for certain, that a change is something you should be worried about? Or that it’s just business as usual?


If you can’t deal with noise, then you fundamentally cannot become data driven.


Imagine that you don’t need to ask your data team for some fancy analysis. You can just plug numbers into some tool, and be confident that:

  • Things are ok, it’s business as usual, or
  • Things are not ok, go investigate!

Wouldn’t that be nice?

XmR charts are a 90 year old solution that will give you that confidence.

More importantly, you can use it on your own. No need for fancy software. No need for a degree in data science. Give it a minute before you reach for some fancy maths.