how do I add a column to my existing gradbook
Mark, you can add a Notes column by clicking on the gear icon in Grades and then selecting, "show notes column." Otherwise the only way to add a column in the gradebook is to created a graded (and published) assignment under the Assignment link (on left the left side of your course nav links) - How do I create an assignment shell in an assignment group?
Hope this helps!
Retrieving data ...