I didnt know that. I already started turning with the auto turner i made. My whole incubator is home made but i think i have done a great job on it so hopfully my hatch will will hit at least 50 percent.I also read that you should put shipped eggs upright like in an egg carton and not turn them the first couple of days in the incubator. I didn't learn this until after my shipped eggs already started. That may account for so many not developing and poor air pockets on so many in the beginning, I now have 6 out of 18 in lockdown. I sopped turning on day 16 instead of day 18 which was recommended for shipped eggs. I hope they all hatch, but I don't know.