i dont understand how this site works.
it says to enter "miles since last fuel-up..." but then it calculates those miles as how much you drove on THAT fuel up...shouldnt the "miles since last fuel-up" go towards the previous gallons you filled up??? help me understand please!
First, take a deep breath. No, you're not doing anything wrong. Sorry you're confused.
Fuelly is calculating how much fuel you used for the distance you just drove by calculating the difference from full. So the fuel you just put in tells Fuelly how much fuel you used since the last time you filled up. Does that make it more clear?
Take a water jug and fill it to the top. Now pour most of the water out without measuring it but leave some in the jug. How do you find how much water you poured out without measuring what's left in the jug?
Now take a measuring cup and fill the jug back to the top while keeping track of how many cups you needed to do so. Let's say you had to use 14 1/2 cups to fill the jug back up. Well that's how much water you poured out in the first place. You had to replace it with new water to find out how much you poured out.
Okay, now imagine that your fuel tank is the water jug. When you drove around you used fuel--like pouring the water out. When you went to the gas station, the pump measured how much fuel you needed to replace what you used on your trip--like when you used the cup to measure how much water you needed to replace what you poured out.
So while it's true that the fuel you just put into your vehicle will be used on your next trip, it's a pretty accurate way of measuring how much you used on your last trip, as long as you fill up to approximately the same level each time.
Presonally, I always fill to the first time the pump 'clicks' off.