That's somewhat interesting, but if I use my adjustable measure and bump it up in 5 gr increments, it would seem that even if it wasn't the actual volume indicated, I would still be increasing / decreasing by a consistent amount. When I find the best one, that'll be "it" regardless of how accurate the number on the side of the measure. In relation, yesterday, while shooting my BP rifle, I compared the spout on my rifle flask against my adjustable measure...30 grains on one matched the other.
This is very similar to how I reload smokeless rounds using my Lee Disk powder measure. It works by volume using different sized cavities. Even using different LOT numbers of the same powder within the same cavity will give differing grain weights.