The only traces of this ingenious medieval device, installed in 1357, are 13 wooden beams jutting from the wall above street level. Each held a brass bowl, into which a metal ball would drop from the window above, to chime the hour. The clockworks were inside the building, powered and regulated by a water cistern that drained at a steady pace. The clock was built along with Medersa Bou Inania across the road, to track correct prayer times.
A designated timekeeper, a mouaqqit, regulated the clock. There were similar clocks across the medieval Arab world, including another in Fez at the Kairaouine Mosque, which had a similar structure in the Dar Mouaqqit tower adjacent to the mosque's main entrance. The brass bowls have been removed for preservation, for use when the clockworks are eventually restored.