iwc GROSSE INGENIEUR CHRONOGRAPH Mode D'emploi page 23

To ensure that your watch continues to function perfectly, you should have
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it checked by an IWC service centre at least once a year. Your watch should
also be tested after exposure to unusually harsh conditions. If the tests
are not carried out as stipulated, or if the watch is opened by unauthorised
persons, IWC will accept no warranty or liability claims.
Recommendation: Your authorised IWC Official Agent must carry out
a water-resistance test whenever your IWC watch is opened and serviced.
Servicing your Big Ingenieur Chronograph
Although the parts in this watch are all manufactured from top-quality
materials, a number of components are subject to natural wear and tear. It
is particularly important to ensure that the points at which wear occurs are
always well-lubricated and that oil contaminated by metal abrasion is
regularly removed. For this reason, we recommend that you have your
watch serviced approximately every five years. Please contact an
authorised IWC Official Agent or send your watch directly to the IWC
Customer Service Department in Schaffhausen.
Effective from January 2009.
Technical specifications subject to change.