Compass

A compass was a device used to determine direction on a planet. The simplest kind was a magnetised dial that would point to the north pole of a planet. Such compasses could only function properly where the planet had a bipolar magnetic field.

A segment of the Key to Time was disguised as a compass. (AUDIO: The Judgement of Isskar)

While shopping for presents for her TARDIS companions on 21st century Earth, Tegan found a compass that looked like a fob watch. When she realised some of her money was no longer in circulation, she stole it, rationalising that her future self would pay for it. (PROSE: Last Minute Shopping)