Specifies methods for the testing of optical instruments and instruments containing optical components under equivalent conditions, for their ability to resist the combined influence of cold and low air pressure, including the potential condensation and freezing of water simultaneously acting. Is applicable to instruments designed for operation and/or transport in high mountainous areas or on board or externally mounted on aircraft or missiles. The purpose of testing is to investigate to what extent the optical, thermal, mechanical, chemical and electrical performance characteristics are affected by low temperature and low air pressure.