[stfwn]

That's such a cool nugget of information. The Versailles one is apparently A = 435 Hz, the 'diapason normal'. Nowadays we mostly use concert pitch at A = 440 Hz. The 99% Invisible podcast has a mini-story on it:

https://99percentinvisible.org/episode/mini-stories-volume-8...

They say that after Versailles:

> London’s Royal Philharmonic Society would still tune higher to about 439 Hz though. This was because the mandate specified that Concert A should be 435 Hz according to a tuning fork of a specific weight at 15 degrees Celsius. The temperature was specified so that the metal tuning fork could be accurately reproduced, but British orchestras reasoned that their concert halls were warmer than that, and so to compensate they would tune higher.

I wonder if they tested their assumption with a conformant tuning fork.

[jacquesm]

Apparently their pitch standard was an Oboe at room temperature (20 degrees) which went up just enough to make up that 4 Hz difference compared to tuned at 15 degrees against that fork. It's a neat little hack.