PID-loop tutorial

I use the LOG command output data to "throttle_log", it goes into a file called "throttle_log.txt" which I then rename to something like "throttle.001.log" in the OS. not sure if I can rename it within kOS. Anyways, the code examples have all been tested now.
I don't like Ruby and don't know it well enough to understand this change.  What does it do?