Shell damage is directly related to shell strength. A number of techniques and instruments have been developed to measure eggshell strength. Specific gravity is an indirect non-destructive method. Determining an eggs specific gravity is accomplished by the flotation of the egg in various salt solutions.
Specific gravity is the ratio of the weight of an object to the weight of an equal volume of water.
In other words, weigh the egg and then divide the weight by the volume of the egg. Specific gravity of an egg indicates the quantity of shell relative to other components of the egg. Egg specific gravity usually declines as the hen ages. This is partly due to the size of the egg increasing more rapidly than shell weight. Therefore, differences in specific gravity among eggs of similar weights are mainly due to variations in the amount of shell.