Interesting. 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 freq

Interesting. 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. In fact: https://en.wikipedia.org/wiki/Utility_frequency#Time_error_correction_.28TEC.29 https://en.wikipedia.org/wiki/Utility_frequency#Time_error_c...