It's an experimental way to calculate how "volatile" is a project source code repository, by comparing the amount of dead code (rarely touched) with the amount of actively modified one. More or less detailed theoretical summary is in theory.pdf.

You need to have Ruby 2.6+ installed. Then you install this tool:

$ gem install volatility

Then, you run it:

$ volatility --help

Read these guidelines. Make sure your build is green before you contribute your pull request. You will need to have Ruby 2.3+ and Bundler installed. Then:

$ bundle update
$ bundle exec rake

If it's clean and you don't see any error messages, submit your pull request.