The dialtone is by no means exact. There is a bandwidth in which the dialtone should be.

Made curious by the discussion I checked other sources and finally found a good summary on Wikipedia. The English text seems to be an abbreviated version of the German text.

English: https://en.wikipedia.org/wiki/Concert_pitch
German: https://de.wikipedia.org/wiki/Kammerton

In short the concert pitch travels all about from 409 to 461 Hz depending on instrument, time, and preference of conductor, instrumentalist, or singer.


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