It's Porsche Design Ocean 500 by IWC & the rarer version of the 500 series.

A very rare watch compared to the common titanium Ocean 500 as this is the dark black PVD version. 34mm X 40mm X 9mm.

IWC ref. 37521 ,ETA 2892, 50bar water resist.
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A good read here;

https://www.watchprosite.com/iwc/yes--iwc--no-not-pvd--no-not-military-bund--iwc-ticon-coated-ocean-2000/727.1105183.8280738/

https://www.youtube.com/watch?v=H-wEyeNLZCc

The coating applied was called "TiCon" and was the result of long experiments with two goals: having the watch in black color and also to harden the surface of the titanium.

The process to "TiCon" the watches proved to be a very complicated and fairly costly process but in 1983 they succeeded with an in-house process to nitrocarburate the titanium. The titanium was hereby hardened 40 micros into the surface at a heat of 1060 degreed Celcius and bombarded with various gases. "TiCon" amalgamates the following factors: titanium carbide, titanium oxyde and titanium nitrate. This entire process of blackening titanium is described in the doctoral thesis of David Seyffer, the IWC museum curator on pages 234 to 242.

You can see below the two "TiCon versions at the left and the "normal" versions at the right. Given the fact that the coating is only a few micros into the surface means that with wearing the watch it will over time turn from a fairly concentrated black into lighter black to turn - eventually and in the extreme - back to "normal" titanium color.

*Excerpts in 2012 (price then) from one of a seasoned collector of Bund IWC watches:

The 2000 model seems to be a bit more prevalent than the 500 model. In the past decade I've seen about a dozen 2000 models offered for sale while I can only remember seeing three 500 models offered in the same time period.

Also, be prepared to pay a lot. Because of the rarity, the 2000 models routinely command a 4-5k price and (IIRC) the 500 models aren't much less expensive.
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This one is the small boy size Ocean 500 and the men's one would cost over 4-5 more times.

Porsche Design by IWC, automatic diver with a really nice dial, simple yet militaristic. Crystal is clean and without any scratches. Bracelet is only till 6'3" wrist max fit.

No box papers, no spare links, just the watch only. Asking 1500 euros via Paypal (buyer absorb 4% fees) with worldwide EMS tracked postage included in it (I'll take care of shipping @ Euro 60 value).