AC line frequency has been recognized as a preferred reference for pitch. This is what made Hammond electric clocks the first reliable AC powered timekeepers.
Later, Hammond famously produced electro-mechanical organs referenced to line frequency.
Well, what do you expect from somebody simply following in the creative footsteps of Leonardo DaVinci & Thos. Edison?
I don't think it's a particularly stable reference in the short term. It's true that the power companies adjust it to hit exactly the nominal frequency over a period of many hours, but not at any one instant.
Later, Hammond famously produced electro-mechanical organs referenced to line frequency.
Well, what do you expect from somebody simply following in the creative footsteps of Leonardo DaVinci & Thos. Edison?