Half grade mathematics

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Posted By: Eric Brehm

Of course it is legitimate for a set to have a rating of 6.23, just like it is legitimate for the average height of a group of 20 men to be 5 feet 10.5 inches, even though no one guy has that actual height.

PSA doesn't 'round' to the nearest number. They just use whole (and now half) numbers to designate a certain subjective level of evaluation of quality. There is really no mathematical meaning to it. A 10 is not really 10 times better than a 1, and is certainly not 10 times as valuable as a 1 in general. However, you do get 10 times as many points for a '10' in the registry as you do for a '1'. Your set ratings, however, also depend on the relative value/scarcity of the cards you have; cards which are more valuable (ostensibly, based on PSA 8 values) receive more weight in arriving at your Grade Point Average as well as your overall Set Rating. (The latter also takes your degree of set completion into account.) In cases where all cards in the set have the same weight, your GPA is simply the average numerical grade of the cards in the set, and your Set Rating is your GPA multiplied by your degree of completion.