The GCQuad by itself has the ability to make Carry Distance adjustments based on Barometric Pressure, Temperature, and Estimated Altitude measured directly through the GCQ. To do this, please do the following:
Doing the steps above will allow the barometer data being captured from the GCQuad to be translated to FSX so that the distances are accurate for the readings the Barometer is currently measuring in the environment the unit is actually in.
To practice in real-world conditions, and get data analysis numbers associated with real-world environmental conditions unlike what the GCQuad Barometer is measuring, you can do so, by disabling the GCQuad Barometer option I instructed you on above. From there you can either select REAL-TIME Weather to simulate weather of that real-world-course you're trying to simulate and practice, or modify the condition settings to your likings. For example, you can look up and dial in the altitude, and weather conditions of your local range to simulate numbers you would be seeing if you were in that environment.
Lastly, we also have some helpful articles on this topic, that explain it in a different way, that might help illustrate this mechanism and function better:
I would do some testing with the above information and if you're still uncertain after further indoor testing, I would highly recommend doing outdoor testing to view both the real-life shot distance and the GCQuad distances outdoors.
I hope this helps and provides an understanding of the CONDITIONS function and GCQ Barometer feature of FSX and the GCQuad!