[Waterluvian]

“12 tone equal temperament” is a good string to Google if you want to learn about that. Most pianos are intentionally out of tune just enough that they’re good enough for every key.

Other coincidences that drive me wild: speed of light is almost but not quite 3.0E8m/s And the fine structure constant being almost but not exactly 1/137.

[FreeFull]

Pianos are more complicated, because they also use stretched octaves that aren't just a simple 2:1 ratio, due to inharmonicity of the thick bass strings. There are only a few exceptions, where instead of thicker strings the piano was made really long.

[BoxOfRain]

>speed of light is almost but not quite 3.0E8m/s

On that subject, if you decided to make your base unit of length the distance light travels in a nanosecond it'd almost be a foot but not quite.

[Y_Y]

I know that the speed of light is c, or 1 or 3e8 m/s, but I really feel like it's a foot per nanosecond, because that's how I measured it the lab one day messing around with BNC cables amd an oscillscope.

Similarly the earth-sun distance is 8 light-minutes.These feel right, like measuring mass in stone for people, kilos for sugar, carat for diamonds, electron-volts for particles etc.

[GuB-42]

12 tone equal temperament is all wrong, but never by much, and it is very convenient, so almost everyone uses it.