Cutting it fine?

When is a foot (as in 12 inches) not a foot?  When it's a Subway sandwich apparently.  Somebody posted a picture of one of their "footlong" subs, together with a tape measure showing that it only measured 11 inches.  Now a couple of men in the US are planning to sue Subway claiming that both have been sold subs of less than 12 inches.  Bit reminiscent of when the penalty for selling underweight bread in this country was so severe that bakers would err on the side of caution and add an extra bun, loaf or whatever to an order to make sure they gave too much rather than too little.  This of course is where the definition of a "baker's dozen" as 13 comes from.  Subway are trying to make out that "footlong" is merely a description rather than a guarantee of length, but I don't think that will fly and they may have to do something similar and ensure that their large subs are always more than a foot, in which case we may find the definition of a "Subway foot" as say 12½ inches entering the dictionary.