Cable tensions are also important to proper Autopilot operation. If the cable tensions are too low, the AP Servo has to take up too much slack and so will tend to overcontrol - if they're too tight the servo may have difficulty overcoming friction in the control run & thus providing enough torque to control the hydraulic power drive units effectively. The correct cable tensions are normally given in the Maintenance Manual & checked on the production line prior to first flight & in service at major checks.