Where Adam Neely tests the tunings musically, Benn Jordan does the bibliographic work. He takes the assertions that circulate about 440 Hz — that it was imposed for sinister reasons, that 432 Hz is the frequency of nature — and traces them back to the sources people cite, then to the sources those sources cite.
His framing in the description is blunt: finding how a trend started sometimes leads you to disturbing places. The 440 Hz conspiracy narrative has a documented history in political propaganda and fringe publishing, and a claim's genealogy is relevant when the claim is being repeated as fact.
For a cymatics site this is directly load-bearing. Any rig that displays a tone will eventually be asked to display a healing frequency, and the honest answer is that the pattern on the plate depends on the plate, that 432 Hz produces a different figure from 440 Hz for the same reason 431 Hz does, and that none of this evidences a health effect. Jordan is the reference for where the surrounding folklore came from.