Gauges - Scles -- What the Heck?

I have a bunch of soon to be dioramas sitting around waiting to be finished.  I jumped on the eBay to look for some plants other than grass.  Only a few things to see by looking at scale. So I jumped in the model railroad section and there was a lot to see - all set up by gauge.

I had a model railroad as a kid. When I bought something for it, all I had to look for was HO on the box and I had my item.  But now I have a 1:20 scale model.  What gauge would that be? Had no idea. 
Doing a little web surfing, I was able to make this handy chart. Some gauges I never heard of, but if I need that scale *whatever* I know where to look. 

Hope this helps someone else.