A little while back I wrote about the conventions of CBGs to be tuned in I V I tuning and that a I III V or I IIIb V tuning made more sense to me. I wasn’t sure what order to put them or whether or not to use the flatted third.
Thinking about this more, I got curious about the relationship between strings on a standard tuned guitar. The bottom strings are G B E. Assuming E as your root that maps to IIIb V I. This blew my mind. That means that a standard tuned 3 string guitar is also openly tuned. For quick reference, that maps to Bb D G.