What you’re writing doesn’t make much sense.
Are you saying that the meter says one thing but really is something else? Can you post a picture of it?
At the moment I can’t take the picture. But what I noticed was that VU-plugin (which had nominal level -18 dBFS) output in master channel showed 0 same time in as the master meter in Cubase showed 0. It was for me a suprise since there is no mention about this in the manual. I thoght that 0 in master channel means 0 dBFS.
Well I don’t know what to say then. In Nuendo my meter goes to a maximum of 0dBFS (actually it may have +3 for True Peak overs). It sounds as if either there’s a preference set differently, or the version you’re running is different, or the plugin has an offset that makes 0=0.
I’m assuming btw that the VU plugin has a maximum level of +18VU, and has a red area that goes to +3VU like most of them do.
Here is the picure. Nominal level -10 dBFS (not -18 like I formerly thought) corresponds 0 in master display.
Very hard to read that picture, but I would guess your problem is that you’re measuring using pink noise rather than a sine wave. A VU meter measures average level and whatever peaks are generated are “smoothed out” differently than the very fast response of the output channel.
So instead of setting your signal generator to pink noise use a sine wave. Actually, you can simply use the Cubase test generator plugin (I assume your version has it), set it to sine-wave and then make sure it’s got the same value as your nominal level on the VU meter. I would probably set both to -18dBFS, but whatever, -10dBFS should be fine.
Do that, then look at the master and see if it isn’t closer, or even exactly the same.
Sine wave. Not pink noise.
You’re right, so with sine generator sending 0 dB seems to be nearly equally zero in master, and the VU-meter goes tightly to red. So the voltage is much higher. Pink noise resembles more music mix with all the frequencies. But I get with these different signal sources the same level from master channel but different level from VU-meter. I know that this sound stupid, but how can I mix or especially master with master fader monitor without VU-meter? Probably not very well. Must use ears. 
There is no actual voltage in digital. You have to remember though that you set the “nominal level” on your VU meter to “-10”, so I would expect that the VU meter if the scale continued would be peaking at +10VU.
If you want to test these different points in the signal chain and are using a VU meter you really should lower the nominal level. You might as well set the nominal level to “-18” and then set your sine wave generator to -18dBFS. Then your VU Meter should read “0” and your output “-18dBFS”.
You have to remember that the two meters are measuring level-over-time differently. The VU meter reacts slowly to both increased and decreased levels, and since we perceive things sort of that way it looks “reasonably correct”. Or at least it did years ago.
Your meter on the channels in Cubase however only allow you to adjust how quickly they “fall back” when the signal gets lower, not how fast they react when the signal increases. So you can actually set the meters to have a similar reaction time as a VU meter, but only when the signal drops. This means that the VU meter and the standard meter in Cubase will always look different if you feed them signals with a bunch of short peaks in them, and that’s exactly what your noise has.
I think the obvious answer to “how can I mix” is use your ears. It shouldn’t really be anything else than that I think, at least not for music. Don’t look. Listen.
When it comes to mastering you can forget the VU meter and the channel meter both. Get a good loudness meter instead. Nuendo has loudness metering built in, and you can also find freeware plugins if you go looking. The standard used BS.1770-3 gives you several useful measurements. If you look at the one below I’ll explain what it measures from left to right (this happens to be a surround signal, but that’s irrelevant):
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First is the level for individual channels. The plugin allows you to set the meter scale and timings and peak-hold etc. When I use this plugin to monitor signals I typically use this section mostly to see absolute level and peaks, nothing about loudness.
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The next section gives you actual numbers and they are following what you see in the bars to the right. The values are, respectively;
— Integrated; the perceived loudness measured over the entire range.
— Short Term; the perceived loudness over a short term (I think 3 seconds or so).
— Momentary; the perceived loudness over a short moment (close to a VU meter).
— Loudness range; how wide the range of perceived loudness is over the entire range.
At the bottom there’s a graph with time horizontally and the perceived loudness throughout your range. You can set it so you get the right feedback relative to whatever your target average is, which is shown above and center as the “targets”.
So this meter, and others like it, provide you with a lot better (and more) information than a VU meter does.
Many thanks, MattiasNYC, for this great information and your patience to explain clearly these audio problems. I think I know now much better how to proceed and avoid wasting time and efforts, at least with this matter.