Instruction card popup location: Selects the window where the instruction card popup will appear when you use the "Instructions" command in the main menu. If the window you select is closed when you try to bring up an instruction card, the popup will appear in the main playfield window instead.
Note that this doesn't affect the separate Instruction Card window, which is designed to be positioned on a dedicated instruction card monitor on your pin cab apron. If you don't have a dedicated monitor for that, you can just close the Instruction Card window so that it doesn't take up any display space. (To close it, right-click in the window and select Close from its menu.)