Citizen 2502 Instruction Manual page 5

These watches have the following special features.
1. The register ring which is very important for checking diving time, has the
added function that prevents it from being rotated in the counterclockwise
direction to make it much safer. A register ring that can not be turned in the
counterclockwise direction.
2. The screwlock type crown with double O-ring.
The crown is a screwlock type which uses a double O-ring type with 3 water
resistant packings to improve airtightness and water resistance.
3. The "No decompression limits table" imprinted on the wrist band (There are
some models without this table) to enable divers to dive safely.
The "No decompression limits table" is indicated on the wrist band to enable
divers to dive safely.
4. Helium gas insulation for professional divers watch (Caliber 5503).
The ability to withstand the pressures of saturated diving using helium gas has
been increased.
By using a strong hard screw type fixed glass ring, the watch is safe even on
the off chance that helium gas penetrates the seals.
* The specification of each caliber, can be found in section "I. Specifications".
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