Hi richard1970,

You cannot use TextBox control to do this. You need their texts and convert them into integer or double type for calculation.

Something like this:

Dim totalpounds As TextBox = DirectCast(gvr.FindControl("TextBox1"), TextBox)
Dim total_p As Integer = Convert.ToInt32(totalpounds.Text)
Dim changedpounds As TextBox = DirectCast(gvr.FindControl("LastAmount"), TextBox)
Dim total_c As Integer = Convert.ToInt32(changedpounds.Text)
Dim lbs As Integer = Convert.ToInt32(DirectCast(gvr.FindControl("lblLbs1"), Label).Text)
'... other control

If total_p <> total_c Then
 cases = total_p \ lbs
End If

If you use different data type for total and other values, just change to Convert.othertype() method to cast.

Thanks,