If you are interested in fuel mileage, keep a log of gas purchased and miles travelled and wait several tanks before calculating overall mileage. If you ar worried about running out of gas, one of the dashboard odometers is 'distance to empty'. It's can be a bit optimistic at the start (mine usually shows 560 to 570 miles)., but it gets a bit pessimistic at the end. Determine a number the you never want to see it drop below, and when you are traveling and refill opportunities are scarce, fill before the point where your travels will take you below that point.
With a spreadsheet you can track individual tanks AND keep an running tally of the accumulating, ie: caculate using all the gas and all the miles. I'd agree, any variations in individual tank calcs (due to pump shut-off variation, mainly) quicky cancel out, with multiple tanks.
I just take it as it comes, it's pretty good compared with historical gauges. I remember Dad's first car - a '49 Austin A40 - the tiny gauge was very "approximate", and also jiggled around so much on rough roads or in corners. One car a friend had, read dramatically different on hills depending on whether you were going up or down.
(I keep trotting this out) My folks' '58 VW Beetle, the gauge was a stick. In many ways it was better: seeing a few inches of wet at the bottom has an immediacy.
No, I believe it had the "reserve" tank, a lever under the dash you turned, if/when the engine started to sputter. Here we go: page 11, in the attached Owner's Manual: '58 Volkwagen Beetle Owner's Manual | PriusChat Astounding what's crammed into this book, in less than 100 pages.
As far as I know it came with nothing. I recall my dad popping the hood and using a makeshift stick to check the gas.