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-   -   Partial Fuel-up Calculations Improvements (https://www.fuelly.com/forums/f2/partial-fuel-up-calculations-improvements-927.html)

ryogajyc 03-23-2012 03:19 PM

Partial Fuel-up Calculations Improvements
 
Presently Fuelly does not calculate partial fuel-up(s) and the next full fuel-up. This discards fuel-up MPG which can be calculate by aggregating partial fuel-up(s) with the next full fuel-up.

The Fuelly FAQ states:
"How do I account for partial fuel-ups?
If you can't completely fill up to the top when you're at the pump and you want to track the fuel-up in Fuelly, check the box next to This is a partial fuel-up. This will let Fuelly know that you have a partial tank. Once marked, Fuelly won't calculate MPG for that fuel-up or the next. However, your partial fills will contribute to your overall average MPG."

It is possible to calculate MPG which includes the partial fuel-up. Simply add the partial fuel-up(s) to the next full fuel-up. This works out b/c the the number of gallons used in the partial fuel-up(s) plus the next full fuel-up is the number of gallons used to travel the miles for the partial fuel-up(s) plus the next full fuel-up. It may be useful to denote these (for example, with an asterisk) to indicate that partial fuel-ups were included. This provides better and more instantaneous MPG rather than discarding the partial fuel-up(s) and next full fuel-up.

MMUK 03-23-2012 08:38 PM

Yes, I had to do this on my fuelly tank 34 (it's two tanks added together). There was an attendant who insisted on fuelling up for me for this particular tank (never happened before), so it wasn't vented&brimmed as usual (probably 4 or 5 litres short).

Initially I tried to do it as a partial tank but ran into the problem that you found.

MMUK 03-23-2012 08:48 PM

Adding to what I just put:

I put the detailed figures for both tanks into the notes section, so that I would be able to unpick them in the future.

Ultimately this is something which fuelly could do - if there is a partial followed by a full fuel-up, the partial tank and the following one could be combined on the graph & an mpg figure could be produced for the second tank (based on both tanks together).

pb 03-23-2012 11:03 PM

We can't really do that because Fuelly's individual MPG calculations are based on the difference from full. Partials are not a full tank, and if you combine them with another tank, the size of full changes. So the individual mileage calculation would be off.

We know it's frustrating to not get an individual fuel economy number when you add a partial, but we don't want to provide misleading numbers. And combing full and partials would be misleading because the size of the calculated full tank would be too big. There's more info in this FAQ: Why do I have to fill the tank all the way up every time I buy fuel?

pb 03-23-2012 11:09 PM

Oh, and just to be clear, you mention in your post that "This discards fuel-up MPG..." and I just want to note that partials do contribute to your overall average fuel economy. For your overall average Fuelly calculates your total fuel volume filled and total distance driven. So even though you don't get individual MPGs for the fuel-ups around a partial, they do contribute to your overall average.

ryogajyc 03-24-2012 01:47 AM

"We can't really do that because Fuelly's individual MPG calculations are based on the difference from full. Partials are not a full tank, and if you combine them with another tank, the size of full changes. So the individual mileage calculation would be off."

No, that is incorrect. Fuelly already handles different "size of full" in the smaller "size of full", because no special handling is required. If someone drives to empty and fills up, this is recorded/calculated find. The next time, they fill-up before going to empty, say with half the tank left. The "size of full" is smaller, but the MPG calculation is still correct.

What matters is in the MPG calculation is that the amount of gas correlates to the miles traveled. This is still correct when adding partial fuel-ups to the next full fuel-up. This changes the "size of full" larger, but is still mathematically correct, just as a smaller "size of full" is mathematically correct.

"Oh, and just to be clear, you mention in your post that "This discards fuel-up MPG..." and I just want to note that partials do contribute to your overall average fuel economy. For your overall average Fuelly calculates your total fuel volume filled and total distance driven. So even though you don't get individual MPGs for the fuel-ups around a partial, they do contribute to your overall average."

Yes, I did fully read the FAQ and understand that it contributes the overall average MPG. "Last tank MPG" is a misnomer for what I described, so I used the the term "fuel-up MPG" which is a superset of "last tank MPG".

ryogajyc 03-24-2012 01:48 AM

Correction to my last post: "recorded/calculated find" => "recorded/calculated fine"

MMUK 03-24-2012 02:29 AM

>Partials are not a full tank, and if you combine them with another tank, the size of full changes. So the individual mileage calculation would be off.

I'm having trouble understanding the logic here. Obviously a partial tank is no good for calculating MPG for that tank.

However one (or more) partials followed by a full tank should give you all the data you need to give a combined MPG figure for that subset of tanks. We've all read & understood the FAQ, but it's not relevant to this particular scenario.

MMUK 03-24-2012 02:46 AM

Example:

Tank 1 : 30 Litres 300 Miles Full tank

Tank 2 : 20 Litres 300 Miles Partial tank
Tank 3 : 30 Litres 200 Miles Full tank
Tank 4 : 30 Litres 300 Miles Full tank

If we look at the tanks individually ...

Tank 1 and Tank 4 can be calculated OK (300 Miles on 30 Litres).

Tank 2 is bad because we don't know the true amount of fuel.

Tank 3 is bad because (without looking at tank 3) we don't know the true amount of fuel.

However... What is being suggested here is to effectively combine Tank 2 and 3.

Tank 2/3 : 50 Litres 500 Miles 500 miles on 50 litres.

We get an accurate MPG figure for the combined tanks (although not individually). There is no missing information, both fuel and distance is known accurately.

Fuelly is fine with this at the moment if we manually combine the tanks. Ryogajyc is suggesting that fuelly be able to recognise this scenario and supply a combined MPG figure for the series of partials & the final full.

Now, it is true that this sort of sequence-based logic is difficult in SQL because SQL is focused on set manipulation and not sequence manipulation (I don't know if there is an equivalent to Oracle's ROW_NUMBER or Ingres TIDs in MySQL, but that would make it easier).

pb 03-24-2012 06:28 AM

Fuelly is based on the simple idea of one trip to the pump = one fuel-up. Once we start combining fuel-ups and assigning an average across multiple fuel-ups we start to lose that simplicity and it becomes harder to explain. I understand what you're saying here, and I understand the frustration with not seeing a fuel economy number every time. But we'd rather err on the side of keeping things simple.

ryogajyc 03-24-2012 12:50 PM

MMUK, thanks for providing an example.

pb, I don't follow how "assigning an average across multiple fuel-ups... lose[s] that simplicity and becomes harder to explain" since Fuelly _already_ assigns an average across multiple fuel-ups. It's called "overall average MPG" and it's mentioned right in the FAQ I quoted.

Personally, I don't think it's that hard to explain. Just denote it with an asterisk or some symbol and link to a new FAQ. In addition, it could be an user selectable option. Users who want to combine partial fuel-ups with the next full fuel-up can see such statistics for everyone. Users who do not, see what they see now.

Also, I argue that it does not "lose simplicity"; it actually makes it simpler. MMUK is jumping through hoops right now to make Fuelly report his partial fuel-up + full fuel-up. He has to add them manually and then keep extra info in the notes. With the proposed change, he would simply record the fuel-ups and Fuelly would simply and automatically report it.

MMUK and I would both use such an option if it were available. I suspect many others would too.

pb 03-24-2012 02:41 PM

I think we'll have to agree to disagree on the simplicity and the difficulty of explaining things. There's definitely more than one way to track fuel economy. We'll give this idea some thought. Sometimes changes can be worth overcoming the obstacles to implementing them.

MMUK 03-24-2012 03:55 PM

Sometimes complexity can be removed by use of clever layout. For example, on the 'tanks' section of the vehicle screen, the tanks in a partial-partial-full sequence can be grouped with a vertical bar and inter-tank spacing.

Tank 1 30 L 300 m 10m/L

Tank 2 20 L 300 m | 10m/L

Tank 3 30 L 200 m | (partial)

Tank 4 30 L 300 m 10m/L

Now, to me the above would seem self-explanatory. On the other hand, I think this would be much more complex to implement than it would be to explain (on the implementation side you have to worry about edits which change the sequence or the type of tank, and correct tank sequencing becomes really important if there are > 1 fuel ups in a day, whereas before it just causes problems with the graph).

MMUK 03-24-2012 04:02 PM

PS I'm using 'miles per litre' in the above example, just to keep the numbers simple (it matches the type of data I normally enter, although not the fuel economy units). Here in the UK we have a really irritating mix of units due to our half-hearted conversion to metric in some areas.

ryogajyc 03-24-2012 04:11 PM

First, I appreciate that this will be given some thought.

Second, I think that those people who will have difficulty understanding the underlying details of grouping partial+full fuel-ups are the sort that simply use Fuelly and and trust that Fuelly does the recording and calculations for them correctly without worrying about any of the underlying details.

Finally, I think MMUK's grouping tanks makes understanding the basic idea easy, without delving into the details.

DTMAce 03-25-2012 10:38 AM

Sadly, I have been here, done this, discussed this at length with PB over a year ago and things remain the same.

I in fact setup my personal Excel sheet to calculate this some time ago for me, using the data exported from Fuelly into it. Works perfectly, but the sad truth of the matter is I have YET to use a partial fuel up entry on Fuelly. I always fill the tank of all the vehicles I drive. However, should I do an entry on here with a partial, my sheet will calculate the MPG from the subset of the partial(s) + the next full fill up. In fact it will do this for up to 10 partials in a row if need be. And yes it was a lot of calculations in the sheet to make that happen! LOL

I can see why PB would not want to incorporate this for two reasons:

One, it can be a problem such as how many tanks in a row will have to be provided and the extra work in creating the calculations for them to work properly.

Two, it will complicate this for the users who do not care if the partials are individually listed or not, providing the overall MPG averages are benefiting from it. Not to mention that for the tank that combines the partials, the statistics for that tank will be incorrect, regardless whether the MPG is correct or not.

I just find it easier to avoid the problem by avoiding partials in the first place, or combining them on paper before adding the entry on Fuelly. I have done this once or twice for the van, as a result of my other half not filling the tank up when she put gas in it. At least I got a receipt and could calculate the costs and fuel, etc.

JPBroad 04-17-2012 08:25 AM

PB,

I LOVE your work and this is a fantastic tool. Honestly, I've been telling anyone who will listen to go and use Fuelly.

However, having just had the experience of a partial (due to credit limit on a large diesel tank), I do agree that it should work as ryogajyc suggests. This is how I've tracked in the past and, although partial fill-ups ARE uncommon (for me), I certainly expected to be able to deal with it appropriately in Fuelly.

Thank you for your consideration in this issue.

Again, thanks for such a fantastic tool!

-John Paul-


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