Zigzag plotter
From Tardis Wiki, the free Doctor Who reference
The zigzag plotter was a component in the Doctor's TARDIS which looked like a car gear lever. The Eleventh Doctor talked Amy Pond through its use (two steps to the right if one's back was to the door) to stop the TARDIS from being thrown into the Time Vortex with only her inside. (TV: The Lodger)
