This menu item enables the graphic display of slot edges. Some plaques, such as the USC #20 slotted plaque illustrated below, have collimating (ie. gold) slots into which the isotope sources are placed (as opposed to plastic or silicone carriers with omnidirectional slots such as the COMS or ROPES plaques.) Slot type is indicated when creating the slots in the Add/delete patterns... dialog. Off by default.