My first and second batches I started with 41 eggs each. This is the max my turner can handle. Of those 1/2 were fertilized, of those 20 I got 15 hatch. I lost 3 after pipping and one that hatched but was lame and later died. I had 2 that looked good til the end. Filled up the egg except for a small air pocket, they were peeping and rolling the egg, but never pipped and died. I felt I should have helped but read that you should just let nature take it's course. It's a hard road to take some times. My first batch in the little giant is a still air and came with a thermometer. I added a thermometer and hygrometer and they were always about 3 -4 degrees different. Of course one was at the top of the egg, one at the bottom. They hatched on day 21.
My second hatch all happened on day 20, with the same machine and no controls were changed from the first time around. I got 16 out of that one, but only 1 that was fertilized and never pipped.
So, each batch is different, it's a learning curve that you love and hate at the same time.
Good Luck, keep trying.