Centering specifications vary between grading companies. Professional Sports Authenticator (PSA) is the most lenient - 60/40 centering on the front and 75/25 on the back are the general guidelines for what could be considered a Gem Mint 10. Beckett Grading Services (BGS) is the most strict - requiring 50/50 on both the front and back to be eligible for a grade of 10*. Sports Card Guarantee (SGC) and Edge Grading are somewhere in the middle with SGC being very strict on the backs of cards (55/45 front and back) and Edge being very loose with the centering requirements for card backs (55/45 front, 75/25 back).