title: Silverlight datagrid elapsed time cell
body: <p>In my silverlight application I use a data grid. I have a column with session started time and a column with elapsed time. The elapsed time is "total minutes : seconds". In my model I have a property ElapsedTimeDisplay that compute and transform the elapsed time into a string. 
  How can update that each second? 
  Is there any possibility to update only that column?
  Is there any other possibility of achieving this without using a trigger?</p>