Do you have a handheld microscope? The 30x to 60x are about $10 at Radio Shack and you'll be able to watch the trichs change colors. Clear is not ready, cloudy is best for the 'head high', while amber is the body stone.

At least, that's what I'm told.

The trichs, or golf balls on a tee, are really easy to keep an eye on. I was able to do it on my first grow with the microscope right out of the box.