color of the trichomes is the only true test for harvest. pistils change color whenever they want, mine turned brown weeks before I harvested by following the change in the trichomes. 30-60X pocket microscope (with built-in light) is best. Go by the average color of the trichs, over the whole plant, top, bottom, middle. I sniped very, very small samples from the bud leaves and placed them on a white paper plate for viewing, at least three samples per plant.

Hope this helps....enjoy.