AC Voltage: Fluctuation?

[PDK]

I've got a Monster Power HTS3500 (I know, its been covered ad nauseum) which has a voltmeter on the front. Granted, I really don't know much about electricity other than I pay the power company for it. Usually, it reads at 120 or 121 but this morning it was hovering around 125 or 126. Is this a large or unusual level? I'm guessing it isn't because the dial isn't pegged but couldn't help but wonder about it. Why does this happen and is it cause for concern?

[Resident Loser]

...my local PSC(or PUC for others) a fluctuation of 10% is not abnormal as it is "overall load" dependent...higher(or lower) numbers for extended periods of time may be cause for concern...

jimHJJ(...FWIW...)