Just take a ruler and measure them across(diameter) and measure how high they sit in the pan/plate. Should give you a good idea of the difference in size, even if it's in millimeters. Crack one of your eggs now and put it in a bowl in the fridge(it won't rot in 2 wks time....the eggs in the store are much, much older than that). Should still show a good visual two weeks later of the difference of one of your previous eggs compared to your present eggs.
why not just select an average-looking egg now, seal it whole in a baggie to prevent evaporation, store it three weeks and crack it with a "hen warm" egg on the same day?Take a picture of it too. Two days sitting in the fridge, I imagine the yolks would fall at least a little bit.