We just added a new 2017 vehicle our stable. What I didn't find was a place to put the starting mileage which was 14. Unless I put in an incomplete fill up with the vehicles starting mileage, I miss one full fill up. This is not only pertinent to brand new vehicles, but to used vehicles that people purchase.
Are you using odometer reading or trip reading method? There is no initial input required, just fill up and either take note of the mileage then, if using odometer, then when you come to fuel up again, input your mileage and fuelly will do the calculations. Same with trip meter, reset when refuelling, take note of the miles driven next time you fill up. If you add 14 miles with no fuel as an "initial" fuel up, it will mess up other stats like "average miles per tank" etc.
Inputting starting mileage without a fill up will lead to an error in the calculations. A full tank from a dealer isn't a courtesy everywhere, and the full tank that there might be might not actually full. Granted the impact of this error will lessen as fill ups are added.
A starting mileage entry will likely not change how odometer readings for the calculations change; the first one won't have a result, and is just form setting the start point.
When I get a new to me vehicle I go to the nearest station and fill it even if it's new from the dealer with a supposedly full tank. It may only take a few pints but at least I know I'm starting with a full tank. Then I reset the trip odometers and I'm set from then on. I input all my data from trip odometer miles since the last fill.
2016 Honda CR-V EX 2WD Mountain Air Metallic