Preloader rotation help!

so, I can make a normal preloader, with a bar and percent shown and so on… But I want to make a little thing in the middle of the preloader that rotates faster and faster when the percent loaded goes up.

This is what I thought would work:

_root.spinner._rotation += (bytes_loaded/bytes_total*100);

but it just spins slowly, not increasing its speed…
I’m stuck…

thanks in advance!