Bet you've never seen one of these. This is a reference 3651, and it's a waterproof, round-pusher chronograph – from the 1980s! Many believe the aforementioned 1463 to be the only vintage waterproof chronograph, but in fact, the '80s yielded one more reference. Consider that in the '80s we saw minor upgrades to classics, like the 2499/100 and the 3450 (both seen above) and though the world of mechanical watches was still in something of a lull, Patek would make these special watches for special clients. The 3651 is perhaps the most special of these very special watches. It uses the same caliber seen in the 1463 from the 1950s, but the rest of the watch is completely different. The case is chunkier, the bezel completely flat and wider, with larger pushers and crown. Only two of these watches have ever surfaced, with sequential serial numbers, and production dates to 1988! Yes, 1988. The origins of the 3651 are unclear, but it is believed that a very small handful were made for Patek's best clients. Only two have surfaced, Jason believes there are likely only three of them in the world. You are looking at pure unobtainium, people.