A card can not have an overall grade more than .5 above the lowest sub grade.
There are exception to that rule however. 10,10,10,8.5 have got 9.5 overall to give you an idea..
Some of the sub grades can hold a higher weight then others when getting a bump to a full point above the lowest grade, EG= Edges. when the rest of the card is near perfect or well above the lowest grade...