pls add text box for "total gas cost"

[pkpkpkpk]

Additional text box for total gas cost; in addition to the existing parameters : "gallons" & "cost/gallon"
Entering 2 of these 3 should populate the other 1.

I like it because I can remember the gas price/gallon and the total cost is on my credit card statement ( from mint.com). I dont have to remember the actual gallons pumped.

[Aerten]

And I write down the gallons and the total amount spent... but not the price per gallon.