This part of ISO 9022 specifies methods for the testing of optical instruments and instruments containing optical components , under equivalent conditions, for their ability resist salt mist. Exposure to salt mist mainly results in the corrosion of metals; effects may also occur by way of clogging or binding of moving parts. The purpose of testing is to assess as early as possible the ability of the instrument , and particularly of the surfaces and protective coatings of instrument , to resist the effects of a salt atmosphere . Normally , representative samples or complete small units are used for testing. Complete large instruments or assemblies are only tested as specified in this part of ISO 9022 in exceptional cases.