I’ve said this before, but it’s worth repeating: Utilities deliver three things: voltage, frequency and reliability. The first two items impact the third. And, frequency – at least in an interconnected system with plenty of inertia like what we have in continental North America – is pretty easy to manage because it’s the same throughout the power system. Here in the Western interconnection where I live, that means the frequency is the same in Denver, Las Vegas, San Diego and Vancouver, BC.