Very interesting. Of particular interest to me because all the eggs of appropriate size went to a hatchery of the chickens my parents raised when I was home. We were very careful with ours and made every effort to avoid thin shells, cracks or other apparent physical problems including small eggs, extra large and those that might be double or more yokes. The consistent hatch-ability percentage for our flocks eggs were 95%. These were broiler chicks. This was in the mid to late 1950's.