I am not clear on what you are describing as far as the Master-Details goes. What comes to mid for me is 2 grids, a master grid and a details grid. Clicking in the master, sets the data in teh details. If you set things up using a DataSet with two DataTables and a Relation, then you can implement a Master-Details as two grid by setting DataSource/DataMember on the grids. Here is a sample
that shows master-details-details (three grids and two relations).
Here is that sample modified with a column of numbers in each grid, and labels on the form holding the sum of those columns. It does this by adding up the values whenever you type into one of the columns, or when you cahnge the parent grid (forcing new content into the child grid).