Look towards the bottom of the article that says "WINNERS". It gives a description of what you should be able to see in the egg around Day 7. If you click on the link to the pic, you'll see a pic of an egg that has the characteristics of the description. Hope that helps.
basically in the first couple of days you should see small clusters of veins by day 7-10 you should see a shadow of where the developing chicken is.
i am new to incubating but a lil research go's far lol hope it all turns out for you