Years ago I researched the dialtone as a frequency standard. What I found out was that although it may appear to be very close to A-440, it is not guaranteed. And each central office has their own dialtone generator. So the dialtone in Madison, Wisconsin is not related to the dialtone in Kansas City or in Oakville, Ontario. And in some rural areas served by little independent phone companies, the dialtone is completely different and does not have anything like an A-440 in it. So, the bottom line is that I would trust a good tuning fork at a known temperature more than I would trust the dialtone as a pitch reference. -Robert Scott Ypsilanti, Michigan
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