Selecting Initial Object using Stack 
Use
In order to simplify processing, the system saves the last used objects of each user
and lists them in a stack.For every object (for example, material), the system saves the last ten objects that were exploded in the product structure for each user. If you want to display one of these objects again, you can use the Stack function when you enter the key fields.
Prerequisites
The stack function is only active when the following prerequisites are met:
See:
Product Structure BrowserProcedure

When you want to change the
Settings for the product structure explosion it is recommended doing this before the selection of the initial object. After selecting the initial object the system explodes the product structure.
If there is no tab page for the object you would like to display, check the active filter. When the filter settings does not allow this object type to be displayed, you must first use another filter or no filter at all.
You see the tab page where the key fields for the selected object type are entered.

The function
(Stack) is on the tab page when you have exploded the object of this type at least once.
You see the dialog box Last-used <object type> (such as Documents).
Result
The system explodes the product structure using the filter settings.
You can navigate within the product structure or use it to execute other functions, for example, to copy change objects to a change master record, or documents to a recipient list.