If I can put two bob's worth in, I'd say that while measures that assess and compare sky conditions undoubtedly have use, in the end they are irrelevant to simple enjoyment of the hobby. Even a newcomer quickly learns to assess his/her sky conditions at home by looking up, and you can easily tell whether it's going to be a bad, good or cracker night's observing.
Human's are funny in that we seem to need to overcomplicate things - not just that, we need to invent complexity and jargon to control the field! This is why we end up with a multitude of scales, all invented by earnest people with a wish to stamp their imprimatur on observing through a telescope. And astro equipment. And astro-imaging.
Don't even worry about it, unless you want to join the rat-race. Just plonk the telescope on the back lawn, whack in an eyepiece, and marvel! Err, provided the transparency is better than 4.0 NELM or 20.5 SQM and the seeing is whatever on the Pickering scale, or is that Bortle, or is that 1-5?
Gimme a break!
Cheers -