The charged engrammeter is a device given to the player by Kharshai during Children of Mah. He asks you to retrieve his memory of Zamorak's betrayal of Zaros from The Empty Throne Room. Once the five memory springs have been harvested, the engrammeter is labelled (full) and it can be returned to Kharshai at the ritual site. If a partially or completely full engrammeter is destroyed, all the memories must be recollected, after retrieving a new engrammeter from Kharshai.
At any time when full it can be operated. If you are not near or inside The Empty Throne Room, you are told to go there. When near the entrance or inside, the engrammeter will emit various levels of hums or whines based on how close you are to Kharshai's memory springs.