The point of transition between the densities within an octave that operates according to what might be perceived as a three-dimensional clock-like face stretched across the entire galaxy. As the galaxy revolves or spirals, each constituent solar system and planet moves through the scheduled density of experience. The cycles move precisely as a clock strikes the hour. Upon completing a density, or cycle therein, those who have successfully learned the lesson of that cycle are harvested in order that they may ascertain whether they are ready to graduate to the next density. This is perhaps somewhat analogous to passing a final exam at the end of a grade in school in order to move onto the next grade.