This remarkable little timer uses temperature instead of time to perfectly gauge whether a boiled egg is soft, medium or hard. It absorbs heat exactly as an egg does, changing color from the outside edge in to show the level of doneness. Rest this ingenious plastic egg on the pan bottom and it will change color as the boiling eggs progress from raw to soft, medium or hard boiled. Adjusts automatically to the number of eggs and the level of water in the pot. Easy to use and extremely reliable.