When installing a valve positioner it is always recommended that gauges be installed on the positioner. During normal positioner operation gauges have the benefit of showing air movement between the ports on the positioner and the actuator. The main benefit of having gauges on a positioner is during calibration. When a positioner with gauges is calibrated the gauges can be used to determine movement and end of travel of the actuator.  The gauges will indicate when the positioner is loading air into the actuator instead of relying on the change in the sound of the air output or visually noticing the actuator moving.  Another time it is beneficial to have gauges on the positioner is during trouble shooting. The instrument gauge will determine if the I/P is outputting properly on a electro-pneumatic positioner or if it is receiving a proper signal on a pneumatic positioner. The output gauges can also help determine if an actuator is leaking. A positioner with gauges has the benefit of helping to both calibrate and troubleshoot positioners as well as to give a visual indication that the positioner is moving air during normal operation.