Big Cy ~
I bet you wish you had left me outta this! You know I'm a trouble maker from way back!
Anyway ... please bare with me on this one as it's a little difficult to explain. A typical poultry ranch (which is different than an egg ranch) would produce fertilized eggs and sell them by the truck loads to the hatcheries. The hatcheries would do the incubation and, of course, the hatching. Okay fine. But let's back up for a minute ... To insure the hatchery got it's money's worth, most poultrymen would include additional eggs because it was common for some eggs not to hatch, (dead chicks inside). And for anyone (poultrymen or hatcher) to determine the status of a chick inside, whether it was fertilized, dead, or whatever, they would "candle" the eggs; which at one point was a literal candle, and later on they started using candling "lights." So irregardless which candling device was used they could immediately tell if the egg was fertile, plus the growth status of the chick. (Dad recalls candling eggs by the "thousands!")
Bottom line ...

No one along the line would need a scale of any kind to determine if an egg contained a chick. And while I'm on the subject, a "pullet" is a female chick that offically becomes a "hen" once she starts laying again to produce ... 1. More fertilized eggs. Or ... 2. Eating eggs.
And where does the rooster fit into all of this? If you don't know the answer to that one then I recommend we go back to page one and start all over again.
Please note; I'm not trying to be a wise guy, nor upset the flow of this thread. And hopefully you are getting as big a kick out of this as I am. Plus, I would say the item in question has been fully identified right from the get-go.
So the question still remains ... What's the story on the conflicting weights for various sizes of a dozen eggs? Dad doesn't have the answer and neither do I. I think I will run down to the grocery store with my camera and see what I can find. I just hope the "eggman" in the store doesn't think I'm weird.
Respectfully,
Bob