Un-masking a ring for preloader?

Hey guys, I was wondering how to make one of those nifty circular preloaders, the one where the ring goes all the way around while it preloads and I was thinking I might do it by Neil’s Tween AS preloader tutorial (if theres a better way please tell me :)) but I’m running into some problems… first of all… how do I create a mask that I can alter shape so that it tweens to unmask the circle?

Remember, if theres a better way to do it, please tell me :slight_smile: