What mileage does your slant six powered ride get?

I fill my tank to the brim and drive it as daily as I normally do daily, after two days I go back and fill it back up to the brim and take a look at the amount of gas it to to fill it back to the brim, take a mileage reading and do the math, then if I take a trip 200 miles or a little less, do the same, about the closest I can get.
That' prob the best way to do it. For example, I filled my car up, drove 176 miles, filled it again. Took 5.9 gallons to fill it back to the top of the tank. So I take 176 miles, divided by 5.9=29.8 MPG. Then you can keep a running log, each time you fill it, then average all readings.