Newbie question: creating a variable from system data

[RobertFrazierAnderson]

I'm wanting to have an item on my watchface that changes based on system data, in this case AQI. I can put a widget up on my WF that has a type of "hmUI.data_type.AQI", but how do I return the actual value of AQI to a variable that I can use to control my display?