With respect to Magna Carta requiring that there be one unified measure of volume, and another for length, thus unifying disparate measurement systems used to trade each different commodity, there is an argument made that this supposition is in error, and that it actually required these remain separately defined measures, but each be consistent across the kingdom: In several of the subsequent confirmations of this charter, which, for successive ages, attest at once how apt it was to be forgotten by power, and how present it always was to the memory of the people, the real meaning of this 25th chapter appears to have been misunderstood.
The object of the whole statute was, not to innovate, but to fix existing rights and usages, and to guard against fraud and oppression.
To have prescribed that there should be but one unit of weights and one measure of wine, ale, and corn, would have been a great and violent innovation upon all the existing habits and usages of the people.
It regulates in like manner, the price of the gallon of ale, by the price of wheat, barley, and oats; and finally, declares that, "by the consent of the whole realm of England, the measure of the king was made; that is to say: that an English penny, called a sterling round, and without any clipping, shall weigh thirty-two wheat corns in the midst of the ear, and twenty-pence do make an ounce, and twelve ounces one pound, and eight pound do make a gallon of wine, and eight gallons of wine do make a London bushel, which is the eighth part of a quarter.
"[4]Adams goes on to say (paraphrased and simplified): Thus, the key to the whole measurement system of 1266 was the weight of the silver penny sterling.
King Henry VII had 43 copies of the Exchequer standards made and distributed to the principal cities of the kingdom, but these were later found to be defective, and remade in 1496.
Adams explains that this act of 1496 made several errors including inverting the order of the old statutes, assuming that the penny sterling, described in the acts of 1266 and 1304 was the penny weight troy (which it was not because the coinage had been adjusted since), and a belief that it was the measure, and not the weight, of eight gallons of wine, which constituted the bushel.