Vacuum in the manifold drops as engine demand increases. If you use ported vacuum you always have a vacuum signal. If you want to make adjustments it can be done using the advance pot on the distributor when you use ported vacuum.
The decreasing or waning phases are when the moon shrinks from the full moon down to the new moon (darkness). As the moon wanes during the 3rd and 4th quarters, this is a good time to prune plants, as the water table is diminishing and so less sap will flow out of the cut ends.
Link on the names below for your monthly Full Moon Guide! Note: The Harvest Moon is the full Moon that occurs closest to the autumnal equinox. It can occur in either September or October. At this time, crops such as corn, pumpkins, squash, and wild rice are ready for gathering.