check the odbfs thread in the video forum..
b.t.w., in the us, in broadcasting, ovu is -20 dbfs, or +4 dbu

no zero in digital means ''stop ''and zero on the vu is average youcan turn it up more

I'm sure there must be tons of threads on this subject, but to make it quick.

With a reference signal of 1kHz sine 0VU=-20dBFS in the US and -18dBFS in Europe.

Be careful, a musical signal will register differently. that is because the sine wave of the 1kHz tone has the same energy in its positive and negative half. A "musical" signal is a different story.

A VU reacts very slowly (much like your ears) and a peakmeter much faster. Some digital meters show you the instant value of the sample.
They will never agree with e/o and that's the point. Very nice to have both side by side because they give you an idea of loudness, versus a technical reading that helps you prevent overshoots.

In digital you abbreviate dBFS FS stands for Full Scale.

Also, this might help:

http://www.prorec.com/prorec/articles.nsf/articles/EA68A9018C905AFB8625675400514576