A rotated-die error comes about when the obverse and reverse dies are not aligned properly with respect to each other.
Any normal US coin will always display a correct upright orientation for its obverse and reverse designs as long as you keep flipping it vertically ("heads over toes").
Even though many collectors today use the term, "rotated-reverse error," to describe the incorrect alignment of the reverse die with respect to the obverse die, it is not quite an accurate term to use. According to The Error Coin Encyclopedia by Arnold Margolis and Fred Weinberg, it is often the case "we do not know exactly which die was incorrectly oriented in the press."
There are three possible causes for a rotated-die error, as follows:
- 1. Incorrect installation of the dies.
- 2. Incorrect grinding of guide marks, which
leads to incorrect installation.
- 3. Loose die rotating in its recess.
The first two causes would lead to repetitive, stable occurrences of rotated-die errors in coins, while the third one would create dynamic, non-repetitive errors found in coins.
In some instances, both stable and dynamic errors can arise during the same press production run. A die could be rotating loosely (creating a series of varied rotations), and then a technician can tighten it up in the wrong position, leading to a series of consistent rotations.
For the Rotated Dies Table, CW is the number of degrees the reverse design is rotated to the right of the 12:00 o'clock position (after flipping the coin vertically from the obverse side). In a similar vein, CCW is the number of degrees the reverse is rotated to the left of the 12:00 o'clock position.
Rarity values as used in the Table are excerpted from www.rotateddies.com with permission.
R-8: 1 - 3 known
R-7: 4 - 12
R-6: 13 - 30
R-5 : 31 - 80
R-4: 81 - 200
R-3: 201 - 500
R-2: 501 - 1,000
R-1: Over 1,000
Data for the last two columns in the Table are obtained from CONECA's website. A "Variety" name and UVC (Universal Variety Classification) are both assigned to each error reported to and verified by CONECA.
The total number of known rotated-die varieties thus far compiled here is 17.
Please do report any findings to Ken here.
Many thanks go to Mike Diamond for his helpful input for this introduction.