Some tanks are irregularly shaped, so the level on the stick (and sometimes the gauge) is not indicative of the true percentage of capacity. So then you have to find a way getting the tank empty, then mark the stick as you put known quantities of fuel back in.
Our friend's Gulfstar 44 has a cool folding stick from the factory that is calibrated accurately. The distance between certain amounts of gallons varies as a result, tank is molded into the centerline of the hull. Our old Hatteras had the same issue, with centerline tanks. Fortunately a PO (or perhaps it came from the factory that way) had calibrated on-tank gauges that were quite accurate. There were little hatches in the lower companionway that made reading them simple.
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George
"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"
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