From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
The Pendulum Room is a room in the Heavenly Realm.
The Pendulum Room allowed a person's mind to travel to any place at any point in time.
Dragon Ball Z
Chaozu, Kuririn, Tenshinhan, and Yamucha used the room in "Pendulum Room Peril" and traveled over a hundred hundred years into Planet Vegeta's past. They fought against two Phantom Saiyans, Scarface and Shorty, in order to train. It was revealed that it was impossible to be killed in the Pendulum Room despite the events that occurred in the visions the room induced.
The Pendulum Room was named for the huge pendulum swinging back in forth in it. The pendulum swung over a ring which a person had ro stand in if they wished to be transported by the pendulum.
- The Pendulum Room only appears twice in anime filler episodes and never returns in future episodes.
- The Pendulum Room does not exactly allow the user to travel back in time in a typical sense, their mind is joined in an outward manifestation of what each person believes everything to be.
- In the 11th episode of the Imperfect Cell Saga, "Up to Piccolo", Mister Popo refers to the Hyperbolic Time Chamber as the Pendulum Room. This is an error.