The candling of eggs is performed to determine whether or not the eggs are fertilised. Although straightforward mistakes are still sometimes made. These mostly occur when the pencil torch is shone on the wrong part of the egg, viz., the airpocket end. Another error occurs when the candling is performed too early. The best method involves candling after 4 to 5 days. What you must then determine is represented in the photos below.
The first photo shows an infertile egg, the second a fertilised egg and the third a candled egg after 4 days.
Do not be in a hurry to remove the eggs that are shown to be infertile and allow the hen to hatch for about 10 days. This will ensure that the hen receives an adequate rest between hatchings