Fair enough. I guess what I was trying to say is measuring by weight is more accurate, but you must have a baseline weight to weigh to. If you don’t know what your target weight of mixed fuel is to be, there is no way to measure by weight blindly. Using a given volume - say 10% of 1 gallon of Klotz techniplate; or 12.8 fluid ounces (378.5mL) will weigh 379.2g (@1.002g/mL). Now if you weigh a given mixed fuel volume at (hypothetically) 3400g, Your 10% oil by volume is actually 11.1% by weight. So if the recipe changes at all, your final weight is going to differ. You’re pretty much relegated to using volume in some fashion no matter what, but knowing the densities of the components makes it really easy to weigh it out and be really accurate. I have yet to meet an engine that ran adversely different if one of the components is off by a fraction of a percent. A dyno will likely be able to show the difference, if it’s sensitive enough.

Benol weighs more likely because it has a few additives in it making it denser than virgin castor.