That’s were the cell phone calculator comes in! What I tend to see, along the same lines is,
10oz Widget munchies $3.99 39.9 cents/oz
2lb Widget Munchies 11.99 $6.00 /pound
Frankly, I think that has more to do with how it was entered into their computer system rather then anything on purpose. Especially when then next item says
2 pack of 3 lb boxes Widget Munchies $32.99 $16.50/unit
In order for the label to spit out a good comparison, the person making the label would have to convert all things into the same units.