Disc

The "disc" was an artifact in the collection of the National Museum. The museum's curator, Marcus Brody, requested that Indiana Jones try his hand at researching the object from Allen dig-K as the museum's people failed.

Noting his findings in a 1935 journal, Jones was unable to determine where the powerful object had originated from though he thought it was from an extremely advanced civilization. While he couldn't determine what the disc was for, it reminded him of Tibetan monk prayer pillars, and as such suggested that spinning it would release the artifact's secrets. He considered it to be a conveyance for knowledge after wondering whether the disc was used for ritual ornamentation or as a signalling device.

Jones supplied a list of instructions for the disc's use as the artifact wouldn't function without specific rules being observed.

Behind the scenes
The disc was created for the PC's instruction booklet by Gregory Harsh of Beeline Group which provided the instructions from an in-universe perspective via Indiana Jones' journal for the year 1935.