When picking out eggs at the supermarket, most of us check the "best by" date, but it turns out those other numbers listed on the carton may be the real key to avoiding some very bad eggs.According to the FDA Guide to Federal Food Labeling Requirements , eggs must include the product name, manufacturer's name, official identification, the U.S. Department of Agriculture (USDA) approval number, ingredients statement, net weight statement, and nutrition information.But the FDA doesn't have any jurisdiction on how expiration dates on eggs are listed . "FDA does not require food firms to place 'expired by,' 'use by,' or 'best before' dates on food products," the FDA states on its website. "This information is entirely at the discretion of the manufacturer."This means that your supermarket could technically sell you food past the expiration date. It also means you may not really know how fresh your eggs are.But not all hope is lost, as Cosmopolitan reported, those triple-digit numbers underneath the "best by" date, which range from one to 365, are called the "Julian date" and reveal what day of the year the eggs were placed in their carton.This number — while not required by the FDA, is required by many states — can be helpful to those who don't want to solely rely on the "best by" date and don't mind doing a little math.