[euromodder]

For my diesel car, I can't recommend a ScanGauge.
The average gets thrown off way too much by changes in driving behaviour.
I've long had the feeling I'm calibrating the SG to my driving, rather than to the actual fuel being used.

The SG doesn't respond well to DPF regenerations either.
When that happens, AVG suddenly improves quickly - I think it's not counting the diesel being post-injected.

I use it mostly for LOD, intake and coolant temperatures (intake T clearly shows the DPF regenerations), while the 4th spot is variable, often VLT or trip AVG, but the later is getting less popular as there's so little correlation with the real world.

On very similar commutes, trip AVG will range from 5.4 (44) tot 3.8 L/100km (62).
That's simply not happening.

Amazingly, total fuel used is often very close to the actual value.