Your persnickety line is precisely why you would use Gold instead of commodities for the comparison. The appreciation of Gold is perhaps the best stand-in for

Your persnickety line is precisely why you would use Gold instead of commodities for the comparison. The appreciation of Gold is perhaps the best stand-in for the value of technological progress since then (including financial technology, e.g. if the Roman held onto that gold to from then until day). And to be really persnickety, staple purchasing power is hardly a ruler for enormous wealth.