Zigzag plotter

The zigzag plotter, or triple vector zigzag plotter, was a component in the Doctor's TARDIS console which looked like a bus automatic gearbox lever.

When the Fourth Doctor had mis-set the triple vector zigzag plotter, Romana II corrected it. (PROSE: The English Way of Death)

The Eleventh Doctor talked Amy Pond through the plotter's 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)