The only gauge I found to be wrong was the boost pressure. It has never registered more than about 5PSI. Scangauge shows it correctly.
Other gauges are pretty accurate including the fuel gauge.
Before I got the SG, I was keeping detailed records on fuel. My manual calculations revealed between 8 & 9 MPG. After a few trips with the Scangauge, it agreed pretty closely with my calculations so now I just rely on SG.
I sent my X-Gauge listing to Scangauge and they responded with 3 additional X-Gauges:
Cruise Control set speed (MPH)
Transmission output shaft speed (RPM)
Power Take Off Set speed (RPM)
So now, I'm looking for a plow to hang off the back... Maybe make some cash on the side...