^{The Longevity or Useful Life of Stouffer Step Tablets and Gray Scales}

^{Stouffer Step Tablets and Gray Scales are made under controlled conditions to meet or exceed the requirements for archival permanence following procedures recommended by the manufacturers of the materials. Archival permanence is usually defined as 50 to 100 years or more. Studies at the National Institute of Science and Technology have shown that the densities of this kind of step tablet will remain stable for at least four years when handled and stored with care.}

^{The primary causes of degradation are use, followed by ( in no particular order) heat, humidity, fingerprints, splashes including spittle, chemical fumes and vapors, attempts to clean the emulsion with anything other than a soft camelhair brush, and abuse.}

^{A quality control device that is handled 40 times a day will degrade faster than one that is handled once a week. The user should set a routine to determine the frequency of replacement based upon factors occurring in-house and the foregoing discussion.}

^{Users that we are aware of who have /or are establishing procedures for ISO 9000 Certification are specifying replacement every six months.}

^{ISO 9000 Accountability}

^{Stouffer Transmission Sensitivity Guides / Step Tablets are made according to these specifications . Densitometry readings are made on a densitometer that conforms to ANSI Ph 2.19 1986 and validated by reference to Standard Reference Material 1008 from the National Institute of Science and Technology. Our densitometers are returned to the manufacturer every six months for re-certification.}

^{Stouffer Reflection Step Tablet Traceability} 

The density values for the Stouffer Reflection step tablets were derived by using an X-Rite 528 reflection spectrodensitometer calibrated in accordance to spectral responses defined by National Institute of Standards and Technology using 45°/0° Reflectance geometry. This instrument meets the traceability guidelines required for use in an ISO-9000 Quality Assurance program. Density measurements were taken at the center of each step and are valid in this area only.

The X-Rite 528 reflection spectrodensitometer used is returned to the manufacturer on an annual basis for certification and re-calibration.