Air Quality Monitor input voltage dependant

I have 2 identical arduino setups that I’m trying to use as a reference and measurement but they aren’t giving the same baseline. When hooked up to the usb input they give a lower output than when on vin. Currently they are tied in parallel to 5v on the arduino nanos’ vins but they’re still giving a different measurement. How is the output / the number the arduino gets tied to the input voltage and can I untie it?

I’m using the provided library and have added a couple of displays and a wireless module but they are both set up the same so it shouldn’t affect it.