The rating of a particular recording or storage medium’s ability to retain its data in a readable form over time. The specific measurements and criteria by which various media are judged depend on the type of media. For example: digital audio tape (a magnetic media) has different standards than analog audio tape (also magnetic media) or digital video tape (magnetic). Film and optical media also have their own sets of archival stability criteria. Archival stability specifications are determined by manufacturers and independent labs through a combination of estimates based on past performance and testing designed to simulate long term archival situations where the readability of the media is mapped before and after such that a judgment can be made about its stability over time. As such archival stability estimates are generally not much more than a well-grounded guess when pertaining to a type of media that hasn’t been around very long.