answer:I always fill up the tank when the marker is at the ¾ mark. That is because gas stations here are few and far between and there are odd and fairly regular power outages. No power, no gas. The marker is indicating slightly less gas than what is in the tank. In the snowiest parts of the winter, I usually try to keep ½ tank always. And when I pump, I stand upwind so I don’t breathe the fumes.