IWC Schaffhausen Da Vinci Mode D'emploi page 27

In order to ensure its perfect function, your watch must be tested by an
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IWC service point at least once a year. Testing must also be performed after
exposure to exceptional stresses. If these tests are not performed as
stipulated, or if the watch is opened by unauthorized persons, IWC will
decline any warranty or liability claims.
Recommendation: Your authorized IWC Official Agent must carry out a
water-resistance test whenever your IWC watch is opened and serviced.
How often should my watch be serviced?
The optimal service cycle for your IWC timepiece is exclusive to your watch
and unique lifestyle. The necessary interval between services will be
determined by your individual wearing habits; frequency of wear, your
environment/s, and the intensity of physical activity you engage in. Your fine
mechanical timepiece is an extension of yourself and will run well for as long
and smoothly as it is treated. Therefore, we simply recommend you to
continue wearing your watch for as long as pleases you and to only entrust it
for a service if you notice a deviation from the regular performance, function
or timekeeping. It will then be our pleasure to reinstate the premium
performance with the suitable service.
Status January 2009.
Technical specifications subject to change.