Iterating through rows in a DBGrid

Hi

I have a DBGrid on a form with MultiSelect set to true.  When the user selects various rows and clicks a button, I want to add up the values in one of the columns.  I have no problem isolating the column involved, but how do I iterate through the selected rows?

(I tried making a derivative of the RxDBGrid which has a protected procedure GotoSelection(Index).  I tried to publish it, but got the error "unsatisfied forward declaration")

Any help would be appreciated.

Regards

John