TubularCorporation

Sort of, but it;s also double the low end of the average resting human heartbeat, which is the biological part of why tempos of 60-70bpm or 120-130bpm are so common across so many cultures across so much of history.

The first bass player in my first band was named Karl Marx, not joking.

I didn't ahve any luck tracking down the ETS bit and actually edited my post to change "about 1000 years" (which was easier than saying "the European Middle Ages") to "500 years ago" because what I DID find was a modern typography article that excerpted it in a way that made me second guess my memory. The ETS page you linked describes exactly what I'm talking about, it even starts with an image of a 1:1 ratio page (which makes a 2:1 ratio spread) but I did mess up and call it an octave instead of unison.

That's a different thing, that's absolute sizes not proportions. But also music related.

I can't find a good online reference, The Elements of Typographic Style has a whole short section on it. The basic idea is that sometime in the 16th century they started correlating the ratios of page dimensions to musical intervals, i.e. a 1:1 page would be an octave, etc. Airwindows Chris has his own system: https://www.airwindows.com/airwindows-nodal-tempo-guide/

While we're on this line of discussion, we should keep in mid that scale degrees in European music theory also correspond to the height and width ratios of standard page sizes, or at least they did about 500 years ago. So if you like it oldschool that's important.

If we're talking Western music theory, I'd say a single cycle would be a bar not a beat since the bar is the repeating pattern, so 120bpm in 4/4 would more practically be 0.5Hz IMO.

Don't forget the only difference between tempo and pitch is the range it's in (ignoring scale temperment and stuff like that, which isn't really useful at sub-audible frequencies), the basic rules of harmony can apply to tempo well and historically were

69 bpm