When I worked on DC-8's, we had a different nominclature for the tabs, although the operation was pretty much per Jetlagged's discription. On the elevators, the inbd tab, actuated by the control column thru cables to a bellcrank in the tailcone which operated a pushrod thru the elevator structure to the inbd tab, was known as the control tab. A tab mounted just outboard of this tab, on the elevator trailing edge, was known as the gear tab. The gear tab was also called a boost tab. It was actuated by 2 pushrods connected to the stabilizer rear spar, which caused the tab to react in the opposite direction that the elevator was moved. Note that when the elevator was at neutral, both of these tabs were also neutral. During T/O when the pilot pulled back on the column (we will assume the elevators are now in a faired position caused by airflow), this caused the control tab to be actuated downward, pushing the elevator upward, and thusly pushing the tail of the acft down. The gear tab would also actuate in a downward direction as the elevator moved up, thus creating a boost on the elevator.
Not as easy as originally perceived