[GreenKeys] Tone frequency history?

[Jim Haynes]

On Fri, 8 Oct 2021, Nick England wrote:

> I wonder why 425 Hz tuning forks would have been common? Musical A is 440
> and A-flat is 415.3. 
> Maybe 2125/2975 came first and then 425 tuning forks? Hmmmmmmmmm. 
> Nick
> 
I remember an article about building yourself a 425 Hz frequency standard,
since so few of us had access to frequency counters in the early RTTY 
days.  The musical standard then and now was A=440 Hz, but in an earlier
time it had been 435 Hz.  And there was someone who had a supply of 435
Hz tuning forks for sale.  So what we were supposed to do was carefully
use a rattail file at the crotch of the tuning fork and file away just
enough metal to bring it down to 425 Hz.