Boeing Column Input Clarification
As stated above, the Boeing columns are mechanically linked through a breakout that allows relative motion if the force applied to the link exceeds the breakout level.
Separate sensors measure the positions of the left and right columns. For the non-FBW models and the FBW models operating in Direct Mode, left column position commands the left elevator and right column position commands the right elevator. On the non-FBW models the command path from column to elevator actuator is via mechanical cables (plus the manual reversion path on the 737). On FBW models this command path is via electrical signaling.
For Boeing FBW models operating in either Normal or Secondary mode the flight control computer receives data from both the left and right column position sensors. The average of the left and right column positions is used to drive the longitudinal control laws. In Normal and Secondary modes both elevator surfaces are commanded to the same position.