Od roku 1936 jste si mohli v USA každou hodinu naladit svůj hudební nástroj podle rádia WWV, protože stanice vysílala komorní ´A´ (440 Hz) právě každou hodinu jen za tímto účelem. Nenašel jsem nikde, jestli něco podobného fungovalo i u nás. Btw - zvuk, který se pouštěl k monoskopům v televizi byl 1kHz (teď jsem si stáhl dvě videa monoskopů z youtube změřil to :)
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The US time and frequency station WWV broadcasts a 440 Hz signal at two minutes past every hour, with WWVH broadcasting the same tone at the first minute past every hour. This was added in 1936 to aid orchestras in tuning their instruments.[
The 440 Hz tone (A above middle C) was added to the broadcast in August 1936, at the request of several music organizations.
History of Radio Station WWV | NISThttps://www.nist.gov/pml/time-and-frequency-division/time-distribution/radio-station-wwv/history-radio-station-wwvA440 (pitch standard) - Wikipediahttps://en.wikipedia.org/wiki/A440_(pitch_standard)