> At the urging of singers, the French government made the tuning A = 435 Hz officially standard in France in 1859 Did they know that the time that they had ch

> At the urging of singers, the French government made the tuning A = 435 Hz officially standard in France in 1859 Did they know that the time that they had chosen exactly 435 Hz? That is, were they to directly count the number of waves per second using the technology available at that time? My quick searching says that devices such as "Scheibler's Tonometer" did exist at the time. These allowed the user count the much slower "beats" between two tuning forks, letting them extrapolate the frequency of a unknown tuning fork from a known. But what did they use for a known? Or was the French standard only actually defined as a particular tuning fork, only determined to be 435 Hz at some late time, when better technology was available?