This part of ISO 10109 is applicable to optical instruments and instruments with optical assemblies in extreme conditions of use. It specifies requirements to be met with regard to the resistance of the optical, mechanical, chemical and electrical properties or performance data of instruments to environmental influences and hence determines geographical and technical areas of application. Environmental test methods, as specified in ISO 9022 (all parts), are assigned to the various areas of application for the purpose of ascertaining the suitability of the instruments in their respective area of application. This part of ISO 10109 is the basis for the specification of environmental requirements and environmental tests in instrument standards. If necessary, these requirements and tests can be amended in the instrument standards. This part of ISO 10109 does not deal with the requirements to be met by the packaging of the instrument during transport from the manufacturer to the user.