Zigzag plotter
From Tardis Wiki, the free Doctor Who reference
In it's sixth version, the Doctor's TARDIS had a component called the zigzag plotter which looked like a car gear lever. The zigzag plotter only worked if the operator stood in a specific place while using it. The Doctor talked Amy Pond through its use to stop the TARDIS being thrown into the Void (DW: The Lodger).
