B737 Yaw Damper
The yaw damper gauge reflects the inputs of of the yawdamper. these inputs are not fed back to the rudder pedals, which is why there is an indicator.
The yaw damper system can move the rudder a maximum of 2 degrees (-1/200), 3 deg (-3/4/500), 2 deg (NG flap up), 3 deg (NG flap down), either side of the trimmed position.
You will need the GSA-55 to connect the gauge to the simulator.