I remember how cool it was when stores started putting "extra" information on the shelf tags to make comparison shopping easier. This was, of course, years ago.
I've been slowly putting together a price book of all of the "everyday" prices at stores in my area for the things I buy regularly. The first time I took my note sheet along, I was far too trusting. I thought to myself "Well, they list the break down on the tag on the shelf!". I ended up coming home with a sheet scribbled all over with prices and weights and volumes. Some time later, with the help of a calculator and a lot of patience, I had the pricing broken down into usable form.
Not surprisingly, the best prices are on weird combination. As an example, the 3.8 ounce box of Splenda is the best value at my local WalMart - by about 5 cents an ounce. No one buys that one, because the "price comparison" information lists "price per pound" (which is insane) while most of the other sizes of Splenda list the "price per ounce". Too hard to do the math on the fly, people just ignore that option and choose from the others.
I didn't have time today to check other items, but I've noticed it in the past with Olive Oil, Coffee, Cheese and other staple (for me, anyway) items. The best price is one of the choices that is listed differently from the others. I'm going to do a little research over the next week or so and see what I find out. In the meantime, if you want to comparison shop, take the time to use a calculator - your wallet will thank you.