I've just checked my peroxide and the stuff I use on my piece is actually 2% Vol.7, so I've edited the post above & changed it.

I found this which sort of helps answer your question re Vols.
Though having read it and learned that 'VOL' refers to Oxygen levels, I'm a bit confused myself!

All I know is that I use lowest possible % on my piece and a middle to high % on my natural hair.

LINK:
http://www.using-hydrogen-peroxide.com/h...oxide.html