"% Details" is a rough guide to how much of a coin's fine design details
(such as shield lines or feathers) will be visible in a given grade. It can be
used when more specific guidelines are not available, such as for many world
coins. It does not apply to the outline of major design elements (such as the
outline of a portrait), which should remain 100% visible in grades as low as G-4.
Proof coins, made for collectors with specially
polished dies and coin blanks, also use the 70-point numerical scale with the
prefix "Prf." If a proof coin hasn't been circulated, the minimum grade
would be Prf-60 (or PRF-60).
Within the 60 to 70 range for mint state coins, the exact grade will
depend on characteristics such as luster, surface (bag marks, etc.),
sharpness of strike, and overall eye appeal. Consult a detailed grading
guide for more information.
You should consult a book on coin grading (such as the Official A.N.A.
Grading Standards for United States Coins) if you plan to buy or sell coins
on a regular basis. The ANA also offers grading seminars and classes; see the
ANA website (www.money.org) for more information.
It's important to be aware that coins are only worth "catalog" prices
when the coin is a reasonably attractive, undamaged example of the
grade. Damaged coins may sometimes be "net" graded to a lower grade than
the grade based on wear. If this is done, it should be noted in the
coin's description along with a brief description of the damage.