i know different manufacturing processes do have errors involved which cause "plastic" and fiberglass products to be dimensionaly different after all is said and done. Does this include the common fuel jug? Ok let's assume it does. Then that rules out the idea that all jugs are going to be filled the same. Also throws a monkey wrench into the process for the companies that use the optical sensors to control volume. So that means for it to be consistently accurate when going by volume it would have to be measured before it goes into the jug. If using timers then the preasure in the system has to be the same all the time. Also it takes longer for a bigger volume (expansion) of something to flow thru the same size controls compared to smaller volume(contraction) of the same ingredient at the same preasure.. Are these systems adjusted for different temperatures as to deliver the same volume at a given temp? Alot of things involved. Seems to me the bottom line is two things. Exactly how does a particuliar company control their bottling process and exactly what is the expansion and contraction rates of the ingredients being used? The later being the original question here. It's a Chevy Ford thing. But then we all know that Dodge beats them both anyway!