I am ready to enter my first tank in the database, but I am debating whether to use the value given by the Nav's consumption screen (this is the first tank), or to use the "tank avg" given by the Info display on the speedo?

I am hesitant to use my calculated value, since I don't know how full it was when I picked it up. I also think there can be a lot of variability when filling (and topping off when I do this)...

The info display seems to read a bit lower than the one on the Nav system (33.3 on the Nav screen, vs 32.? on the info display). I forgot to look at it before refueling! Is there a way to see the previous tank's value?

My gut tells me that the value given on the speedo display is more realistic, but I am not sure. I reset the nav system's avg to see if it matches up well with the speedo display.

I might just skip this tank and use the speedo info display for future tanks...

Spiff,

I don't have the NAV system, but I would suggest the manual method. True, you don't know what level the tank was filled to when you received the car so it makes sense to leave out this tank if you want. It's also true that differences in when the pump shuts off may not give you the most accurate measurement for the tank.

However, if one tank reads high because you did not fill up all the way the next one will read low. Even though each tank could be off, over a number of tanks this should give you the most accurate measurement.

Fair enough...

I will try that - I think the "tank average" on the speedometer display might have been pretty close to the calculated, but I topped it off this time....

Thanks,
Jeff

I would use the manual method. It certainly is the most accurate over time and will give you a better feel for how you're doing. I tried to back calculate using the indicated mpg versus my actual and over 6800 miles the gage is about 3 .5 gallons off. That's not a lot of gas but it's enough to have put my average about 0.4 mpg higher than what I'm calculating.

I have tanks that are right on the money and some that are 2 mpg off. Over the long term the manual will give you better numbers. The screen average, assuming someone does not push the all clear button will be a little off. If someone pushes the all clear you're out of the game.

Due to the error I wouldn't mix and match the screen measurement with manual entries as you may drastically under / over state the actual overall.

If you use the "reset" button on the bottom of the consumption screen, I noticed that this will transfer the Avg value (shown right next to the reset button) into the "best" value field (assuming that it really is your best). Is there an overall average as well? I am not in the car (obviously), so I can't remember...

Thanks!

You got me thinking. I'm not sure there is a long term collection. I have not been through all the buttons yet but I assumed a "reset all" button meant it had that feature, but I have not actually looked for it. (I keep all my tanks on an Excel spreadsheet.)

I do wish there was more than one tracking calculation. I was monitoring the overall tank on the dash on a recent trip and I wanted to calculate the overall trip as well as segments of the trip. I don't think I can do that. The reason I wanted to do that was to measure the trip down I79 and then compare it to the trip back. I got 41.5 going down and 40.1 coming back. By resetting each way it I lost the overall trip.

Oh well probably more information than I really need.