This is our first time trying to hatch eggs, and we are on Day 5 with 18 duck eggs in our incubator.
We candled tonight for the first time, and it was REALLY clear which ones were developing and not. We made sure to get a really good LED flashlight, and wait until it was dark, so that we could be sure to see as much as possible.
Pics of developing and non-developing eggs are in this thread (scroll down):
If you buy the high intensity Egg Lume candler from Brinsea, you will be able to see some pretty good detail and movement on the developing embryos. I got mine on sale which they were running a few weeks ago, don't know if they still are. I tried several different LED lights and couldn't see what I can now.