Going for efficiency can be just as involving/challenging as going for power/speed. You'll find quite a few of the members here have/had racing/tuning backgrounds.
I just sucked it up and started conversing in US MPG, too. If you want, you can use the calibration to make it read in MPG Imperial (20% offset on fuel used + your vehicle's actual calibration if needed).
The 80-190+ mpg you're seeing shows you what happens when the engine is at idle when your speed is still high. The
SG doesn't have the ability to show deceleration fuel cut, which is likely a feature of your Escort, and in which case you should actually see infinite MPG when throttle-off. (The closest the
SG gets to infinite is 9999 mpg - which you may see if you do any engine-off coasting).