Detached air cell in developing egg

[HopieGirl4Ever]

Hi,
Recently I candled the eggs under one of my broody hens, and discovered that one of the eggs seems to have a detached air cell (the air cell is off to one side of the egg). The eggs are from our birds, not shipped. They are at day 13 and are all developing fine. I just want to know if anyone experienced this, and how can I make sure this chick hatches? I just would like to know if I will have to help the chick hatch, or should I just leave it... I will take a candling photo later and post it so that you can see how it looks.
Thank you!

 

[HopieGirl4Ever]

Here is a photo. I outlined the egg so you can see it better.

 

[coleco]

My amatuer guess is that the egg in question is much older than 13 days at least it appears much further along to me than that. The air cell is in an ok position for the chick to pip as usual. Perhaps it's just the lighting or photo. Happy hatching