I made some measurements on my 7 level, and sitting, when doing a 2 gallon calibration. I measured with a stick with a small ID tube attached, recording distance from the bottom. Dipsticks made from a dowel rod, a clear tube with an aluminum strip attached were tried and not easy to use or inaccurate. Finally saw a post that used an aluminum stick with holes. I made mine to indicate each 1/2 gal. The holes are staggered side to sideband it works perfectly. The wick effect of anything that goes in the fuel is way higher than the actual level and adversely affected the usability and accuracy. In 100 hrs of recording, the total fill is within 1/2 gal of the dip stick and the totalizer in the G3X. The holes are smaller than 0.063" and it is easy, in all light conditions, to read. You can test the hole size for yourself in a clear glass of fuel to determine what is best. And compared to alternate methods. I hold against the leading side of the fill opening and aft of the internal stiffener.
My strip is alodined .025" X 3/8" and attached to a keychain. Light weight too.
The worst part was wearing the headband magnifier and a vibratory etcher to write the tiny numbers on the stick! If it folded and fit in a shirt pocket it would be perfect, but I have found no elegant way of achieving that yet. Maybe in the shutdown.
One last thing - the absolute reading of a single tank is less than 1/2gal accuracy, but the total of both seems to make up for a tilt one way or the other.