Curious - why food? Why not clothing for a year, or transportation, or the cost of raising a child, or a night at an inn, or what it cost to bribe a Senator? So many simple comparables besides food-for-a-day.
The purpose is to compare pricing across history. Food prices is a good yardstick since everybody throughout history need food. You cant really measure the price of "a night at an inn" for a culture without inns, for example. The cost of transportation is not that useful when most people walk everywhere.
Well, you get the idea. Food is subject to very particular customs, environments and traditions. Much more so than other things. So likely a skewed measure. Got to be other things that make at least as much sense.
