For ALMA Cycle 0, individual project Scheduling Blocks are scheduled for observing taking into account (in rough order of priority): project priority group ("Highest Priority" or "Filler"), the weather conditions and array configuration, source constraints (e.g. availability of target and calibrators), Executive balance, and the number of remaining executions needed to complete an ObsUnitSet. All other things being equal, the project with the highest scientific rank is observed.