I'm currently in the process of building one of these
"A holocron, short for holographic chronicle, was an organic crystal-lattice device, in which the Jedi, as well as the Sith, of old stored phenomenal quantities of data, as well as the holocron's gatekeeper.
This gatekeeper acted as a guide through the holocron's store of information, as a search and recovery engine with a more personal touch. These gatekeepers could relate stories from the holocron's archives to events in the life of the one who activated the holocron. Jedi gatekeepers could sense the ability and level of a Jedi, and offer or restrict information accordingly—so that Padawans were not shown information too advanced and dangerous for their basic stage. Sith holocrons usually had the same restrictive mechanism like Jedi holocrons, but the gatekeeper could corrupt the unawere listener."