For example, I was reviewing some cards I got graded recently. One is a MTG card. Sub grades - Centering 9.5, Corners 8.5, Edges 8.5, and surface 7.5. Add them up and you get 34.0. Divide by 4 (four grades), and you get an overall average of 8.5. CGC overall grade was an 8.
Alot of other cards were like this too. For example I had a Dark Charizard holo that was a 10, 8.5, 9.0, and 6.5 respectively. This also totals 34, and when divided by 4, you get an overall of 8.5 CGC total grade was a 7.5.
What am I missing? Surface counts for a higher chunk of the average when factoring in to the total? Thanks.