Midnight-noon ebb-flow assigns each of the twelve channels a two-hour period of maximum activity, following the classical sequence of qi circulation, and selects points according to the time at which treatment is given. The eight methods of the sacred turtle combine the eight confluent points with a numerical scheme derived from the stems and branches to determine both the point and the time.
Both systems assume that the state of the channel varies through the day and that treatment is more effective at its peak. Modern chronobiology offers some support for the general principle while not confirming the specific schemes. They are worth studying as a demonstration of how thoroughly the classical tradition integrated time into diagnosis.