Telector screen

The  was device which was, for a period of time, present on the Doctor's TARDIS. It took the form of a small screen, and would measure the ship's current position.

The First Doctor on one occasion noted to his companions Ian Chesterton and Barbara Wright that the device was not working properly. Upon exiting the ship, the group discovered that this was in result of the team shrinking to the size of insects. (COMIC: Doctor Who in "Lilliput")