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Message:: [QUOTE="giorgio11, post: 1181516, member: 17094"]If you think about it, hubs are used to produce dies which are used to produce coins. So a hub (or "working" hub) has the same relief as the coin. Raised devices are raised, recessed areas (if any) are recessed. On a die, the relief and left-right orientation are switched. Roosevelt faces left on the die and right on the coin, and the raised areas on a coin are recessed on the die. This makes the production of deep-contrast proof dies, for example, easy, by polishing to produce mirroring in the fields while leaving mint frost on the (recessed) devices. Now, the production of dies requires more than one strike from the hub, and in-between the dies are "work-hardened" or annealed by heating. If a die is struck (more than once, between work-hardenings) by a hub that is not perfectly centered, it will produce a doubled die. If a die is struck by a 1909-dated hub and a 1908-dated hub, it will produce a 1909/8 double eagle, same principle as the 1942/1-P and -D Mercury dimes. So most overdates (from the modern era) are actually classified as dual-hub errors, where the Mint personnel grabbed differently dated hubs between the various "work-hardenings" or annealings required to produce a coin die. (In older coin series, such as Bust halves for example, the Mint workmen would indeed take a die and reengrave the last digit to change the year, often leaving traces of the underdigit. This was a manual operation not involving hubs.) Strike doubling is sometimes called "bounce doubling" for the rebound "bounce" that a die will make in striking a coin. And it is quite common. Hope this helps a bit. There are many experts in this field, and I am not one of them. But I hope I can explain things fairly well in laymen's terms.[/QUOTE]

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