A dart board.
Seriously, though, the first number is major version, the second is minor version, and the last two are basically a really minor revision…like a bug fix. So when they go from 18.104.22.168 to 22.214.171.124 for example that is a functionality update that warrants a new minor version number. But if they went from say 126.96.36.199 to 188.8.131.52 it would probably signify a bug fix and not new functionality. James from Slysoft can probably explain it better considering it’s their versioning system, but, this is how I envision it to work. I’ve been wrong before.