Planchette

Planchette (プランシェット) refers to a type of automatic writing. It is most likely a flat piece of wood that is used to spell out messages or have pencil attached to it for writing, though this is just a speculation. It is unknown on how the Planchette is used in the Toaru Majutsu no Index.

Angel Fall Arc
Tsuchimikado Motoharu references it along with Kokkuri to describe on how Hino Jinsaku takes commands from the writings of his right hand.

Trivia

 * It apparently has no relation to Index's John's Pen Mode, as the kanji used for it can be translated as Automatic Writing.