Topping it off screws my MPG
 

Here in NJ, we pay less with cash. So the attendants more often than not, top it off with some excess gas to round it off to the next nearest dollar amount. This morning, the pump shut off at about 12 gallons+. But the attendant added some more to round the amount to 23.50 resulting in 13.996 gallons. This really screws up my mpg calculation.

How do we work with Fuelly in cases like this? This always happens in NJ.

This happens to me once in a while here in Oregon (the only other state with attendants), but they usually ask if I want it topped off. I always say no.

While topping off will affect the MPG of the current fuel-up, I've found that it averages out over time. I'm not as concerned about a fuel-up here or there as I am about getting a sense of how my car is doing overall. I'd say if you can ask them to stop once the nozzle clicks off, that might be best. Otherwise, if you top off every time, it should be pretty accurate. Just pick one and try to stick with it as best you can.

There's really nothing technically you can do about it with Fuelly.

Yup, just suck it up and understand that there is going to be variation between your fillups anyway - the pumps won't always shut off at exactly the same point. Your average fuel economy over time will still be correct, which is why it would be nice if fuelly would incorporate the ability to plot running averages with user specified # of points to be incorporated into each average. It's essentially the same thing as if you just did a partial fuel-up. The two fuel-ups affected will be dramatically off (one high, one low) but they will cancel each other out when it comes to average mpg.