Maximum number of items at checkout.

An old engineers' joke (told my old engineers):

At the "15 items" checkout, a young man in Cambridge, MA is unloading a
cart 
with twenty five items. Two professors standing behind him note this. One 
says, "He must be one of yours from Harvard, and can't count." The other
one 
replies, "No, he's one of yours from MIT and can't read."

Leon