Checking the quality of your AC

I keep an old-fashioned anaolg voltmeter with a dedicated standard two-prong plug connected to my system's AC duplex all the time. Other than when I first turn on my high-powered tube monoblocks, or when the air conditioning kicks in, I never see any significant sags, and no surges. Sometimes the overall level dips a few volts in the summer when demad is heavy, but most of the time the meter registers about 118v - 120v with the needle being virturally totally steady, including when I am playing the system loud. OTOH, the PLC manufacturers seem to imply that everyone's wall power could be flucuating wildly. Is this meter really telling me something of value?

Thanks Bufus, I realize the voltmeter won't tell me about other AC problems, but I still wonder if voltage correction is really necessary from what I see (or don't see) with this meter.

Shasta - I have definitely gotten audible improvements by using the API Power Wedge products over the last few years, so I have no doubts about there being something to improve upon in AC quality, but these devices can't address line voltage fluctuations, and despite PS Audio and other's hype, I still don't know if that's anything to be concerned about. I have thought of trying out one of the ExactPower AC correction units, which seem like a more elegant approach to the issue than do the Power Plants, but they don't come up too often on A'gon, and I wouldn't want to invest in a new one without knowing what it would do for me (no dealers I know of around here). However, I have read that the guy who makes Equi=Tech products, though he would hardly be unbiased, has said the main thing that the PP's give you is balanced AC (plus filtration of the higher harmonics), and that the rest (meaning a pure sine wave of exactly 120v) is not necessary to correct for under most conditions. From what I've seen from my line voltage meter, and what I've heard from my PW Ultra with selectable balanced mode capability, I might be inclined to agree to a large extent, though I've never brought in a PP to compare with, as I just don't want what basically amounts to another amplifier in my system, and so I can't say I know what 'corrected' voltage and waveform might sound like as opposed to the filtering, balancing, and isolation I already have.