Question 1258: The detective road

A X's Y contains 1 unit more than the standard Y. The earliest reference, but doubtful explanation for the term X's Y dates to the 13th century when Xs who were found to have given a less quantity to customers were punished severely. To guard against such a punishment, Xs would give 1 unit more in whatever they were selling, to ensure not being known as a cheat. More importantly, the practice of making 1 item more was insurance against "short measure", on the basis that one of them could be lost, eaten, burnt, or ruined in some way, thus making it an original legal Y. Thus the origin of the term and the practice.

2 methods of packing for X's Y

 Identify the term "X's Y". No half points.
Answer: XY: The Baker's Dozen. It consists of 13 items instead of the 12 in a regular dozen.