What is machine doubling and numismatics coin

 Machine doubling, also known as strike doubling or mechanical doubling, is a common occurrence in coin minting that can sometimes be mistaken for a genuine double die variety. Unlike double die obverse (DDO) coins, which result from a misalignment of the die during the minting process, machine doubling occurs after the coin has already been struck.

Machine doubling happens when the coin is struck by the die and then shifts slightly before the strike is completed. This shifting causes certain design elements to be slightly doubled or flattened. Machine doubling typically appears as a shelf-like effect on the affected areas of the coin, rather than the distinct separation seen in genuine doubled die coins.

Unlike genuine double die varieties, machine doubling does not increase the value of a coin and is generally considered a mint error rather than a collectible variety. While it can sometimes be difficult to distinguish between machine doubling and genuine double die varieties, experienced collectors and numismatists can often differentiate them based on the characteristics of the doubling and other diagnostic features of the coin.