It is dual purpose, as it lets me know which eggs are the freshest for selling or consuming. They are also labled with a letter which corresponds to the name of the bird. Then they get charted by the day.
Wish I was that organized!!! We just have a big(Huge, really) bowl in the fridge and I rotate them when I sell them. The ones on the bottom go first. One customer takes 3 dozen every 2 weeks or less. But I still have a ton of eggs - we are getting 16 a day now!!
I don't keep them in cartons. I use 24 count mini muffin tins and stack them 3 tall. 72 eggs in less space than 36 in cartons. Just move them up as you take them, as this let's me play with all those gorgeous eggs!