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Old 09-10-2015, 04:41 AM   #31
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Drift? What do you mean by that? The trip odometer uses the same measuring implements as the odometer, so it's just as accurate, and obviously it's reset every tank anyway.
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Old 09-10-2015, 04:49 AM   #32
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The trip odometer has a certain amount of "inaccuracy" because it always resets to zero and loses track of distances beyond the last tenth measured but not enough to tick to the next tenth. Any inaccuracy in using the odometer reading on any one fill-up is negated over time because it never loses track of the "in between" distance measurements.

Yes.. it's a small amount. Yes.. I am nit-picking.

I always tracked my fuel and maintenance info in a notebook in the car. I could calculate details at any point in time, track wear on the tires, total up my expenses, etc. It was manual, but the it was solid. Fuelly has the potential to be every bit as great - it just needs a few more steps taken to get it there.
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Old 09-10-2015, 06:31 AM   #33
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Much of what you're "disputing" here was discussed by me previously in this thread.

Your ownership of a vehicle doesn't match mine, and mine doesn't match the next person. We all have different specific needs. Whether you personally want to track those miles driven is ultimately up to you. I -do- want to track them, though. I'm driving them, and I want them tracked. Fuelly keeps track of more little subtle details than just MPG...
Something came up, and I had to leave the last bit off. Here it is:

Others due want to track those miles though, and after experimenting with setting up a car for odometer reading once, not having a start odometer reading is counter intuitive. So I agree, it should be there.

This is how I see it working if implemented for Fuelly. The system will have a field to enter the initial odometer reading when first setting up the car. It will then ask if you had filled the car at this reading. Enter yes, and the software will treat this as the 'bogus' fill it takes now. Say no, and the software won't start tracking fuel economy until after you put in the first fill into the car. The miles between the initial odometer and that first fill will be ignored for calculating fuel economy and fuel costs, but will be used for any total costs, if such become available through the site.

It will work out this way because a car with a full tank of gas from the seller won't be as full as when a Fuelly user is entering the odometer from the point when the car is actually filled. The car's tank will most likely only be down from the drive back from the gas station and some lot shuffling to finally get it to you. So any error from that and someone entering that initial odometer reading as full will soon be averaged out by the the user fills following. But if you don't use the trip odometer for fills because of 'drift', I have feeling such implementation won't satisfy you.
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Old 09-10-2015, 07:09 AM   #34
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Something came up, and I had to leave the last bit off. Here it is:

Others due want to track those miles though, and after experimenting with setting up a car for odometer reading once, not having a start odometer reading is counter intuitive. So I agree, it should be there.

This is how I see it working if implemented for Fuelly. The system will have a field to enter the initial odometer reading when first setting up the car. It will then ask if you had filled the car at this reading. Enter yes, and the software will treat this as the 'bogus' fill it takes now. Say no, and the software won't start tracking fuel economy until after you put in the first fill into the car. The miles between the initial odometer and that first fill will be ignored for calculating fuel economy and fuel costs, but will be used for any total costs, if such become available through the site.

It will work out this way because a car with a full tank of gas from the seller won't be as full as when a Fuelly user is entering the odometer from the point when the car is actually filled. The car's tank will most likely only be down from the drive back from the gas station and some lot shuffling to finally get it to you. So any error from that and someone entering that initial odometer reading as full will soon be averaged out by the the user fills following. But if you don't use the trip odometer for fills because of 'drift', I have feeling such implementation won't satisfy you.
The issue with "drift" is this: Trip odometers are accurate to 1/10 mile (in the US anyhow), or 528 feet. If I reset my trip odometer and drive 263 feet, it will still show 000.0 for distance. If I do this 21 times, resetting the trip odometer in between each one, I will have driven 5,523 feet, or 1.046 miles and not have ANY measured reading from the trip odometer to reflect any portion of it. In essence, I will have the potential to artificially deflate my MPG by tracking the fuel that was used to travel that distance without tracking the distance actually being traveled.

Yes, this is somewhat nit-picky, but there's no reason to lose the detail simply because of known limitations in how the trip odometer functions. Additionally, this problem can be worse if I do not reset the odometer exactly at the point of fueling (I sometimes am holding the reset button while driving away because the station is very busy).

This is why I use the straight up odometer reading method to track everything - it never resets, it never loses track of any distance traveled because of a reset, and every fill-up I conduct merely increases the accuracy of the overall calculated MPG (263 feet is the MOST that would ever not be tracked on an individual fill-up, and this distance calculated over thousands of gallons becomes a rounding error quickly).

Your description of how the implementation could work is in line with what my thinking has been. If the vehicle is delivered / purchased with anything less than the fuel gauge reading full, drive immediately to the station and fill it so that you can start tracking as close to the delivered mileage as possible.

As far as the tank being less than full, that doesn't matter a whole lot, especially on a new car. I would always set the initial miles to 0 on a new car unless there were more than about 30 on it when I got (which happens if the dealer had to do a swap to get you the car).
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Old 09-10-2015, 01:45 PM   #35
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1.046 miles potential error over 21 fuel purchases averaging, in a Prius, say 437 miles each or 9,177 miles total is an error of 0.000114. And that's if the error is always rounding down each of the 21 times rather than some down, some up, overall basically nothing. How does that compare with the odometer which reads in miles and may be up to .49 miles or 2,639 feet off times 21 fills? Seems like a beam and mote sort of situation.
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Old 09-10-2015, 02:15 PM   #36
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1.046 miles potential error over 21 fuel purchases averaging, in a Prius, say 437 miles each or 9,177 miles total is an error of 0.000114. And that's if the error is always rounding down each of the 21 times rather than some down, some up, overall basically nothing. How does that compare with the odometer which reads in miles and may be up to .49 miles or 2,639 feet off times 21 fills? Seems like a beam and mote sort of situation.
The amount that the trip odometer might be "off" is additive over time. The odometer will NEVER be off more than .49 miles (if it does not read in tenths). Yes, the TRIP ODO will sometimes be reading more than what was traveled, sometimes less. And those amounts could offset one another.

I would imagine that the ODO is actually never allowed to tick to the next mile indicator unless that distance has actually been traveled. So, it's possible that the ODO might be off by as much as .99 miles, but that is still a max amount, never to be exceeded.

Of course, the TRIP ODO might have a similar limitation on ticking off distance traveled. In that case, it could be off by as much as .09 miles at any given point, and be reading lower than actual traveled distance. Again, though, this is a potentially additive shortcoming that WILL build up over time, artificially lowering calculated MPG.
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Old 09-10-2015, 06:16 PM   #37
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It seems much ado about nothing no matter how you slice it.
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Old 09-10-2015, 10:44 PM   #38
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Yea I think you're beginning to split hairs now. You could argue the pumps are not that accurate either, give or take a few Ml when brimming, so even if you could accurately measure all your distances,the fuel amount will never 100% accurate. Fuelly is all about averages, I wouldn't try to be too OCD about it, but that's just me. So long as I know roughly how much my car does to the gallon, and how much I spend on fuel, I'm happy.
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Old 09-11-2015, 02:24 AM   #39
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Because of the way we measure fuel usage and mileage there is an inherent problem with the fuel that is left in the tank, which hasen't been used yet.

One simple solution would be for Fuelly to allow 0 (zero) for Odometer Reading and Fuel used.

You could then use that as your starting fill up.

So, tracking a car from cradle to grave would go something like this:

1. Record 0 miles 0 fuel
2. Fill up (you need to remember this number as it is used at the very end!)
3. Drive
4. Fill up - This second fill up is entered into Fuelly, giving you your first MPG reading
Don't forget that when you fill the car and record the mileage and fuel, you are actually recording the amount of fuel you have just put in, not the amount you used, it just so happens that if you brim your tank each time they are roughly the same and over time the difference will be tiny.
5. Repeat steps 3 and 4 until the car is ready to be scrapped.
6. Don't fill up - drive to the scrap yard, hopefully on the last drop of fuel
7 Record your last mileage reading using the fuel amount from step 2.

Note: If you get the car with a full tank and sell it on with a full tank, you haven't used that fuel so it should not be counted in your records.

Note: If you scrap the car with fuel in the tank, again, you haven't used that fuel, so it should not be counted in your records.

Fuelly could support this model by:

allowing 0 (zero) in the mileage input
allowing 0 (zero) in the fuel input
extra field to record initial fill amount
extra checkbox to indicate this is the last fill (this would then use the value from the initial fill amount.

Oliver.
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Old 09-11-2015, 05:03 AM   #40
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I bought my new car and although it came from the dealer with a "full" tank I filled it. I reset both trip odometers to zero. I plan to keep the car a minimum of 8 years 1 day and/or 100,001 miles. Based on my last 2 years driving experience I anticipate buying fuel approximately 175 times in 8 years and if I go to 100k approximately 250 times. Any errors over such a sampling are insignificant and mean nothing in the grand scheme of life. Now, if the cash in my pocket that pays for things is not in denomination order, smallest outside to largest inside, all turned face up and inserted into my pocket face up with the fold to the left then we have an issue that actually means something to be concerned with.
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