[MetroMPG]

The X Gauge is a way to add a "non stock" gauge to the display screen. EG. you can monitor ECU data that's specific to your vehicle (Prius drivers can monitor hybrid battery state of charge, for example), and you can use it to add "stock" SG gauges, such as adding "Trip AVG MPG" to the "Gauges" display so you can watch both instant and average at once. (I'm doing that in my car - I sometimes have trip, tank & instant MPG up at once.)