had my route measured about two years ago. they sent someone out and had me drive the route as normal, without pulling up to each box. auditor had me reset the trip odometer and back about a 1/4 of a mile to show that the odometer registered both forward and reverse. then went inside the garage were i normally park, reset the odometer again, and drove the route, parking back inside again on return. i gained about .2 , but that was enough to add a mile a day to my ema. if you don't have the exact size of tires on your car as what it came with, you can almost expect the readings to be off 1-2% or even more. (usually listed on the drivers door label)