What specific item needed to be swapped out when moving an astrolabe from London to Cairo to maintain calculation accuracy?

The engraved plate corresponding to the latitude

The accuracy of the astrolabe was highly geographically dependent due to the components known as the Plates, or Tablets. These are removable, engraved discs fitted precisely inside the main body. Each plate is engraved specifically to depict the projection of the local horizon and altitude circles pertinent to a particular latitude. Because the celestial coordinates projected onto the plane of the instrument change based on the observer's position on Earth (their latitude), using a plate calibrated for London while observing in Cairo would yield incorrect results. This necessity to customize the instrument for the specific location highlights a sophisticated dependency: the physical hardware required the correct geographical software (the latitude plate) to function as intended.