A friend of mine turned me on to this link: How Fresh Are Your Eggs? It explains the codes on the sides of egg cartons. What is cool is that you can find out where they were packed (the “P number”) and the date.
The date is a modified Julian date.A complete Julian date is 5 characters: yy + the day of the year. 1/1/2009 = 09001 in Julian and 12/31/09 = 09365 in Julian. The egg cartons leave out the year, assuming that 361 would be interpreted as either 2009 (if we were past 12/27/2009 or 2008 if we were before 12/27. The link that the article gives does this calculation for you.
However, for the geekly inclined, assuming that the 3 digit number is in A1, the following Excel formula will do the same thing for you, esp if you format the cell to show mmm-dd:
The links are pretty cool, esp for the locavores who can tell that my Whole Foods eggs bought in Hadley Mass were packed in Franklin, Connecticut on Jan 7.