Would that be "a calculator"?

~13 for short trips around the neighborhood, 15 on the ten mile drive to work with occasional stops-n-go, 18-20 highway. Drop ~ 2mpg for 4wd.

I went from a 33mpg Corolla to the Blazer so I spent a couple months trying to figure out what was wrong. Before I learned about the fuel gauge issue I even thought someone was siphoning gas from it at night. Just couldn't figure out why I needed to fill up every week

 

and whats the apps method of testing?

my way and the correct from different articles to test it properly is , to fill tank up til it clicks & reset trip on spedo,drive car til about empty,when back @ gas station write down how many miles u drove,refill tank til it clicks,write down exactly how many gallons it took to refill & divide that by ur miles u wrote down & u have ur MPG.

example - drove- 245.3 miles
took- 13.60 gallons to fill back up
divide it- 18.03 average mpg

try and use same gas pump for best accuracy,
this only works though if u have factory size tires or if ur speedo is set correctly for ur smaller/bigger tires.

 

I think there is something off. I mean my 94 bravada is getting 14mpg with all in city driving with all time AWD, an exhaust gas that could even kill a tree, and 211+ miles or in km 339K+

Now wait a minute. you are driving in kmph and have the mileage in km. Are you converting the gas mileage to Miles Per Gallon (or is it liter) or are you leaving it in Kilometers per Gallon (or liters??). It might just be easier to give us your Mileage in ether km or miles and then how much gas you went through.

Sorry but EPA MPG ratings is total BS. 4 out of my 5 other cars exceed the EPA rated highway MPG with mix city and highway. Plus my friends express 1500 conversion van is getting 17mpg with 170+ in city but he Motorkoted the engine along with a K&N air filter.

If nothing seems off driving and no check engine light try air filter and then sparks, wires, rotor, and then see what happens. Try a K&N or spetra air filter. Little more but worth it. and ONLY A/C delco for plug stuff

link to better filters for 04 blazer LS
Discount Air Intake

 

So your "method" is a simple math equation to find the average. Yea thats exactly what the app does for me as well as keeping all my vehicles important info in one easy to find place. And also telling me how much per day, per week, and per year my car is costing me (gas, maintenance, and anything else I put into it). I know its accurate because I can tell down to the 10th of a mile how much further I can go with whats in my tank. I ran out of gas while in line at the gas station once. And thats with my gas gauge being broken and stuck on 3/4 of a tank. But all I have to do is watch the miles because I know exactly how many miles I can go in the city and on the freeway. Only time it gets tricky is if I mix u the freeway and city driving but all that does is make me a little less accurate on how far I can go. Otherwise this app is just as accurate and a lot more convenient than the pen and paper or "calculator" that someone else mentioned.