One other thing worth taking a look through: https://en.wikipedia.org/wiki/Harmonic_series_(music) This contains several super-useful tables that show not only the pitches that happen via the harmonic series, but the retunings necessary to translate the pitches into actual harmonic values. And that math is important to drone works, as you'll want the harmonic tunings instead of the equal tempered ones since the harmonic tunings play off of the series that starts with your drone's "root". Bit of a PITA in hardware, to be sure...but back in the day when I was still singing in choral ensembles, when we had music from the proper period, we would instinctively retune everything note-per-note. And it worked...mainly because equal temperament is a "recent" invention, and when singing something prior to, say, 1700, we'd always tune for that harmonic "blend". With the voice, this is pretty simple (and a bit instinctual, too), but if you want to do this on hardware instruments, you've got to know the retunings and/or ratios.
Please note the digital dickery done to the URL above by the syntax. "series" should be followed by underlines, which MG's forum thinks are "italic" indicators. Silly server, no Pocky.