I just found this on the
PSA website.
PSA Card Grading Standards
GEM-MT 10: Gem Mint
A PSA Gem Mint 10 card is a virtually perfect card. Attributes include four perfectly sharp corners, sharp focus and full original gloss. A PSA Gem Mint 10 card must be free of staining of any kind, but an allowance may be made for a slight printing imperfection if it doesn't impair the overall appeal of the card. The image must be centered on the card within a tolerance not to exceed approximately 55/45 to 60/40 percent on the front, and 75/25 percent on the reverse.
MINT 9: Mint
A PSA Mint 9 is a superb-condition card that exhibits only one of the following minor flaws: a very slight wax stain on reverse, a minor printing imperfection or slightly off-white borders. Centering must be approximately 60/40 to 65/35 or better on the front and 90/10 or better on the reverse.
NM-MT 8: Near Mint-Mint
A PSA NM-MT 8 is a super high-end card that appears Mint 9 at first glance, but upon closer inspection, the card can exhibit the following: a very slight wax stain on reverse, slightest fraying at one or two corners, a minor printing imperfection, and/or slightly off-white borders. Centering must be approximately 65/35 to 70/30 or better on the front and 90/10 or better on the reverse.
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