>>I get c. 100 miles out of the 1st 1/4 tank, so I think "Great, it looks like I'll get 400 miles out of this"
>>By 1/2 tank the trip odo reads c. 150 miles, so I think "Not so good, but it looks like I'll get 300 miles out of this"
>>by 3/4 tank gone it may be c. 210 miles, so I think "Well, I should get 280 miles"
>>
>>But the low gas bing-bing comes on at c. 237 - 247 miles and I usually have to refuel at c. 265 miles (this is mainly all urban - I get 300 miles on the motorway).
>>
>>Anyway, what gives? Does this mean it pays to keep your tank over 3/4 full all the time? I doubt it.
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>But of course! You just did the math. An exhaustive, scientific, top-notch experiment. Of course, I would say instead that it is just the inaccuracy of the sensor and needle system, but that's just me. :-)

Well, considering I do more or less the same route, to-from work, every week, with the odd trip out at the weekend, and have been observing these stats for a long time now, yes, I would say it's an exhaustive observation.

Yes, sure, accuracy of sensors and that vary with the fullness of the tank. But just suppose you were about to enter a 200 mile long desert, no filling station before it or in it, but your tank said 3/4 full, and you'd registered just 100 miles since last fill. You might be a little peeved to run out 100 miles short of your dest.