Gradebook

'grade' = points 'earned' divided by points 'earnable' times 'weight' assigned
'extra credit' = points 'earned' that are not added to points 'earnable'

Unless grades are allowed to exceed 100% (category or course), then extra credit is either:

1. meaningless (in the case where 100% has already been attained)
2. or, merely replacement points for those "unearned" regular points in order to bring the grade closer to 100%

Unless compelled to do so, one need not comment on this assertion... it merely forms a basis for subsequent postings.