Elevator modernization is the renewal of the worn parts of an existing lift while the shaft, and usually the guide rails and counterweight, stay in place. There is no fixed package: on one lift only the cabin interior cladding and door panels are replaced, on another everything except the guide rails. The technical basis for improving the safety of a lift that stays in service is EN 81-80, not the construction standard EN 81-20 that applies to new installations. Whether the guide rails are still true is the single condition that most affects both cost and downtime, because bent rails turn an equipment change into a shaft job.