# The Note "A" = 440.  Why?

**URL:** <https://boards.straightdope.com/t/the-note-a-440-why/423751>\
**Category:** Factual Questions\
**Created:** [October 23, 2007, 8:56pm UTC](https://boards.straightdope.com/t/the-note-a-440-why/423751 "2007-10-23T20:56:18Z")\
**Posts on this page:** 1\
**Page:** 3

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**Author:** ![jovan](https://avatars.discourse-cdn.com/v4/letter/j/0ea827/32.png) [@jovan](https://boards.straightdope.com/u/jovan)\
**Post date:** [November 4, 2007, 10:59am UTC](https://boards.straightdope.com/t/the-note-a-440-why/423751/41 "2007-11-04T10:59:01Z")

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[QUOTE=pulykamell]  
Sure. What it doesn’t quite answer, though, is how they knew and measured exactly 435 Hz, which they apparently had the capability to do since at least 1859.  
[/QUOTE]

The first person to make an accurate frequency measurement was [Marin Marsenne](http://en.wikipedia.org/wiki/Marin_Mersenne), in 1636. Using math derived from Newton’s F=MA, he demonstrated that the frequency of a vibrating string could be calculated knowing the string’s length, mass and tension. You can read about the exact math involved [here.](http://en.wikipedia.org/wiki/Vibrating_string) In his experiment, Marsenne used strings with weights attached to put the strings under tension.

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