One of the most expensive, popular, and desired types of errors are the double denominations. This error happens when a coin is struck on a previously struck coin of a smaller denomination. Examples are a cent on a struck dime, and a nickel on a struck cent. The most dramatic are those with considerable design visible from the original strike. There are a few known double denominations with different dates. The error illustrated here is a 1999 cent on a struck dime from 1997 - 2 years apart!