Citizen 520 Instruction Manual page 19

If solvents, such as thinner and benzine, or substances containing such solvents
come in contact with the watch, discoloration, melting, cracking, etc. may result.
If the watch comes in contact with mercury used in thermometers,the case, band
or other parts may become discolored.
Periodical inspections
Your watch needs inspection once in every two or three years for safety and long
use.
To keep your watch water-resistant, the packing needs to be replaced regularly.
Other parts need to be inspected and replaced if necessary.
Ask for Citizen geuine parts upon replacement.
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