In July 1816, Edward Troughton's 10-foot transit instrument replaced Bradley's earlier one, and reconfirmed Bradley's meridian as the Prime Meridian for the Observatory until December 1850. The telescope itself was regularly calibrated by taking sightings off a number of distant markers. In 1824, a granite obelisk was erected at Chingford, Essex, some eleven miles to the north. The Bradley Obelisk, as it is known, still stands.