when I float eggs I watch for movement.. It will quiver in the water and cause ripples.. some will bounce like a fishing bobber..
to see what I mean, take an egg that you know is alive and float it..
I think it works best in the later stages of developement..
I never mess around with...
I often see people post that an egg died .. they determine it by candling.. Often an embryo does not move as someone is candling.. I wonder how many live eggs are mistakenly thrown away..??
I float test when I am about to throw out the unhatched eggs.. sometimes I will catch a late bloomer that way.. I like floating better than candling.. I seldom do either..