[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, 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. In his experiment, Marsenne used strings with weights attached to put the strings under tension.