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Comment by dcustodio | Hacker News Reader

I fill up every time I refuel and I take notes of the quantity and odometer and the average matches the dashboard.

There is a website you can use to keep track of this: http://www.fuelly.com/

I take a look at my estimates in the dashboard on my Mazda2 (Germany) and also calculate the metrics manually every time I fill the gasoline. Funny thing is, that I tend to use less in the real world then my car makes me believe.

My car tends to value the long range drives on a highway way higher then my average driving habit while commuting. So the higher consumption outliers on the highway tend to skew my results.

What manufacturer and model is that?

I had a 2008 VW Golf TDI Gt Sport (the 140PS PD engine) and that consistently lied. My newer 150 Euro6 (I think) engined VW Beetle TDO gives even better MPG so perhaps it is lying again... Potentially time to measure it versus how much I put in.

How do you measure the distance driven? Perhaps the tachometer is also lying?

Very good point. Odometers (tachometer measures RPM, odometer measures distance) are not as reliable as some may believe, and even if they're perfectly accurate, there are so many variables that it's hard to control. Smaller tires spin faster, which drives up the miles read. Tires get smaller as they wear, so the odometer can be calibrated for new tires but will quickly become inaccurate.

But the odds that your odometer is accurate is very slim in reality: http://www.azfamily.com/story/19769079/tests-show-odometers-...

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