Wow
I forgot to mention here, I added a metro specific wiki page (with an mpguino block):
Metro - EcoModder
I do think it would be more accurate to use the odometer, or the mileage posts if your odometer is off due to tire changes/etc. I've seen the SG come up short before and speedometers are notoriously off.
Generally speaking asian cars will be a multiple of 4104 and gm cars will be a multiple of 5000 though.