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Old 02-03-2011, 11:17 PM   #1
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litres conversion changed?

Has the accuracy of the litres conversion been downgraded? I've noticed that my fuel-ups have suddenly started appearing as 16.001, 39.001 litres etc. They were all displaying correctly until today, I'm certain?
It was much better recently (I was the person who suggested using more dp in the conversion late last year). Please could the extra accuracy be restored?
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Old 02-03-2011, 11:26 PM   #2
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As an example my last fuel up of 16 litres after travelling 141 miles gives me 39.977 miles/UK-gallon. Fuelly is currently showing this as "40.1" MPG :-(
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Old 02-04-2011, 12:19 AM   #3
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We store everything as US units in the database and convert them for display. In that process of converting from gallons to liters, we lose some precision. There's no way around that without completely restructuring the way we store data.
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Old 02-04-2011, 12:20 AM   #4
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And no, we haven't made any changes recently that would affect how things work, so there's no reason for a sudden change.
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Old 02-04-2011, 03:48 AM   #5
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After the 'rounding errors' thread from November (http://www.fuelly.com/forum/mrtickle/comments), Fuelly was changed to add slightly more precision to that conversion without needing to restructure the data. It was a neat solution which worked really well!

Between then and recently, all the fuelups that were whole litres were showing as .000 litres on the website. (I'm sorry but I don't know how to link back to that thread any other way - I think there was a reply by me saying that the change worked well).

Now the same entries have gone back to the pre-November behaviour.
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Old 02-04-2011, 04:07 AM   #6
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Sorry for the double-post - here's the link

http://www.fuelly.com/forum/618/Rounding-errors

I saw the accuracy issue fixed on the site from a few days after that thread, all the way through December and January. (I started this thread as I assumed you had implemented that idea and then something had accidentally rolled it back out).
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Old 02-04-2011, 05:37 AM   #7
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No, we didn't ever implement the changes discussed in that thread. And we haven't changed anything recently.

I don't remember offhand the results of my tests, but I know I was concerned about increasing the size of the database through that change. I'm not sure that slightly increasing the accuracy is worth the extra storage required.

Did you recently edit some of the fuel-ups where you're seeing the problem? On editing, the units go through more conversions: once to display for editing, and then again as it goes back into the db. That can further degrade the accuracy for non-US units.
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Old 02-06-2011, 03:20 AM   #8
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Interesting - yes, I did certainly edit some of them. I didn't realise that just adding a note would would change the value of fuel as well. But thanks for shedding light on why it's happening!

I have deleted the fuelups that I edited, and re-entered them. The "Fuel-up added! Details: " confirmation section displays the fuel to 3dp just as I entered them. But the main page of my car doesn't manage to do that. Perhaps the Details: section isn't reading back out from the Db (just displaying the fields from the form) and the main car page is reading the twice converted value? If so, then that would explain why I thought you'd increased the accuracy back in Nov.
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