If you find a coin at the bottom of the cup when you come back after a long vacation you should toss all the food immediately. It means that the power was out for enough time for your food to melt and re-freeze. If the coin is on top, it means that there was no power failure, and your food is as good as when it went into the freezer. If the coin is in the middle, it means that the power went out for a short period of time and most of your food items are probably still fresh.