A specimen that can be shown to be in the original as-built configuration, or as modified by the user, that remains unaltered from the time it ended operational service. A reproduction built by the constructor of the original artifact in part or in total and having substantially the same type of movement capabilities. The technology of preservation, the scientific investigation of materials, the environment and those things responsible for the deterioration of cultural resources. If the lettering is damaged by an untrained person, a valuable part of history will be lost forever. From these definitions, it can be said that preservation and conservation are similar activities, designed to keep an object in its existing condition while halting further degradation.
Restoration is a more active process that attempts to undo changes caused by past deterioration.
Many conservators will insist that doing nothing to alter the artifact, except to stabilize the further deterioration, is the correct approach. This works fine when the object is to be placed in museum-quality storage with controlled humidity and temperature, away from light, to be used only as part of a study collection. This is the primary reason for restoring a piece of rolling stock. If the artifact has deteriorated to the point that it is no longer suitable for display and much of the original fabric or material has deteriorated beyond the point it can be saved, restoration or reproduction might be the only answer. Sometimes it becomes necessary to replace most of the artifact in order to make it suitable for exhibition.