The Lincoln Cent Double Die is a minting error that occurred at the U.S. Mint in 1955. Manufacturing a die is a multiple step process in which a die is created by striking a working hub which places an image onto a subsequent die that is used to strike the coins. This normally requires multiple blows. In 1955, one of the subsequent obverse dies used at the Philadelphia Mint was misaligned on the second blow resulting in a doubled image. This affected the date and inscriptions which is visible on all of the coins struck from this die. This is historically one of the most famous errors produced by the U.S. Mint.