Sheridan grid problem

[Smithrr]

I have a sheridan grid control with five columns. The third holds amount data. At the bottom of my form there is a text box which should list the total of all the amounts. This works most of the time. The problem I have is if I change an amount and sum again the current row gets counted twice. I just wanted to know if anyone else has tried to do this same type of thing. Any ideas are more than welcome.
Thanks