You've obviously never bought or sold grain. It is done by weight. How is that possible? Because a certain moisture content is supposed and that equates to an exact weight.
If you sell grain today they measure the moisture content and dock the price per bushel if it is too wet.
True. My grandparents were farmers, but I never was in the buying/selling end of it. I always understood it to be a volume measurement. I even looked it up, because I wasn't sure, and it came back as a volume measurement. Then I went to figure how they accounted for different products, because I knew a bushel of apples weighed differently from a bushel of corn or wheat, and found each product was given an accepted weight per bushel.
Kind of a really weird way to get to the value.