Delete sheet 
Using this button, you can delete the selected measurement sheet from the drawings tree view. If the underlying drawing has no more measurement sheets then the drawing itself is also removed from the drawings tree view.
A drawing that has been removed from the
tree view is not actually deleted from the project. When you create a new
measurement sheet (See Drawings/New
measurement sheet) and also, at the measurements management window
(General/Drawings
management 
), you can see and use all the drawings that have been
imported to the project, even if they are not shown at the drawings tree view.
You should close a drawing in order to
be able to delete it.
By deleting a measurement sheet, you
also delete all items associated with it along WITH its measurements which CANNOT be retrieved!