The tanks... have a sight glass right there in the cockpit, so you know exactly how much fuel you have
Are you familiar with the fuel guage in the Piper Super Cub (and I think some earlier variants too)? A sight glass, right there in the cockpit, so you know exactly how much fuel you have... as long as you're in exactly the attitude which the designer wanted you to be in. The aircraft's attitude is, apparently, important enough for Piper to have put two scales on the fuel guage, one for the 3-point attitude on the ground (which will be similar to the attitude you have during slow flight, although it doesn't say so), and one for "straight and level" whatever straight and level meant to the designer. The difference between the two scales is about 1/4 of a tank.
A sight guage can't lie to you, but it can certainly mislead you if you don't know how to read it.
FFF
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