Grainger,
I no longer remember what the acceptable range is, but I blieve it is something from 57 to 63 Hz, and they have to make it up within the 24 hour cycle so that at the end of that period, they have generated exactly 86,400 Hz, ad more often than not, they do this late at night by revving up the turbines a bit. High demand periods are what draw the frequency down (along with the voltage, aand because of the total inertia of the entire system from boilers to the transmission and distribution system, the time constants are pretty long.
I don't remember the exact protocol for adjusting the generator speeds, and it varies based on size, and a bunch of other parameters, but the operators of your local and operating region (you are in SERC), take care of that.
So really, you'd have to monitor the frequency over a 24 hour period and you would typically see peaks and dips in the actual frequency.
-- Jim
Jim Rebman -- recovering audiophile
Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).
s.e.x. 2.1 under construction. Want list: Stereomour II
All ICs homemade (speaker and power next)