Authored by Harry,_Denmark A few years ago I decided to buy an affordable, classic automatic diver. After weeks of study I identified a watch known and respected by all watch collectors, a watch with classic lines and provenance, with an instantly recognizable style entirely its own ? a style capable of withstanding fashion and trends. This watch was the Seiko 6309 diver. Hours spent reading the SCWF archives; Seiko Diver History and the 6309 Buyers Guide lead me to my first deal: a 6309-7049 from Stephen Go. I wore this watch day and night, and found myself looking at the perfection of its hands (unsurpassed in ANY divers watch, in my opinion) the simplicity of the dial and the wonderful functionality of the case. In time, I told myself, this infatuation for the 6309 divers will pass.
"Infatuation for the 6309 divers will pass..."Pictures of that wonderful case, downloaded from the internet, began to fill my hard-disk, desktop and office wall. I traded a mint 62MAS for a IWW?d 6309-7049, and felt guilty about my good fortune
(thanks Mark 
). I began to experiment with straps, ?NATO?s and bracelets. I always returned to the Z-22. I discovered Tokunaga-sans posts on the SCWF and began to understand the mind behind this perfection. "Please touch your own favorite watch with your kind heart and love for ever." Ikuo Tokunaga. I began to realise the 6309 series had been designed by a genius, and was already perfect. In time, I told myself, this infatuation for the 6309 divers will pass.
I bought a YAO dial and hands and immediately realized I would never use it. I bought a Tuna 300m diver, and realized I would never wear it. I traded the Tuna and received my first 6306 diver
(thanks Badrun ), revelling in its rarity. I discovered that after wearing a 6309 every day for two years, looking at my 6309s and my 6306 was just as satisfying as if I had just received them. I completely lost interest in my lifelong grails, the Rolex Sub (so small, so common and yet so expensive) and the Omega Speedmaster (such a pity about the silly tachymeter scale ? why did they not make a rotating bezel version for NASA?). In time, I told myself, this infatuation for the 6309 divers will pass.
But it hasn?t. So I would like to spend a moment to share some impressions of the 6309-7049 and the 6306-7001 Seiko 150m Dive Watches, using two examples from my collection:
Seiko 6309-7049 (left) and 6306-7001 (right).Table 1: 6306/6309 specifications.
For me, the bidirectional bezel is an absolute plus. I use the bezel every day, to mark start points in time: 6 minutes for the eggs, 10 minutes for the lab centrifuge, so my son can track if it is 6pm yet (could be arrival time on a long car trip, or the start of his favourite TV show). So I save a lot of anticlockwise turning by being able to turn clockwise, too! And, lets face it, the "vintage diver" experience is not complete without a bidirectional bezel - after all, how much more exclusive can you get, knowing 99% of the dive watches out there are unidirectional
Notice the weight (mass) of each watch. The 6306 is significantly lighter. Perhaps it has been polished and brushed so much it has lost a lot of case material. Or maybe the case design
is different to the 6309? Perhaps someone who has both models on the same strap would be so kind as to verify that there is in fact a weight difference? The differences in case design may be marginal, but they are there:
Crown comparison. 6306 at right.
Case comparison. 6306 at bottom.Notice the differences in the shoulders of the lugs - they are higher on the 6306. Earlier 6306 cases had a significantly larger crown cut-out, but in my examples the cut-outs appear about the same. Buts lets dwell on the genius of the case for a minute. The crown protection offered by the case is perhaps the most elegant, the simplest and the most innovative ever conceived. It?s what makes the 6309/6 series instantly identifiable, a true trademark design element. Notice also how the planes of the case mould into the arm and the back of the hand. This is the reason why the 6309/6s are as comfortable in use, as wearable as a dress watch in spite of their heft and presence:
"The planes of the case mould into the arm and the back of the hand..."Comparing these two watches is also a comparison of two (almost) identical straps. On the 6309: a Chinese Z-22; on the 6306 a Japanese 6306. The Chinese strap is stiffer, and retains its "bend" in the picture below. The holes in the strap are larger, too.
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Chinese Z-22 strap (top), Japanese Z-22 (bottom).
Chinese Z-22 strap (top), Japanese Z-22 (bottom).The Japanese strap is far softer, more pliant, and lies flat. Both are immensely comfortable, and on the wrist I can feel no difference. Somehow I feel like the Chinese strap will last longer.
Table 2: 6306/6309 beat rates.
I often see technical reviews with lists of data, which at first glance seem dry and uninteresting. But many of these numbers are capable of telling a fantastic story if we can compare them with something tangible. Take the beat of 21.600 bph. Hmm? Nothing? Now consider the equivalent 6bps - that?s really swinging! Or over half a million single, precise beats of the balance and escapement. A day. And we hear of 6309s being used daily for 20 years without a service. That?s almost 4
thousand million beats. Running at a precision greater than 99%. The mind boggles...
Table 3: 6306/6309 jewel distributions.
As we all know, jewels are included in a watch to reduce friction at the main pivotal points of the watch mechanism. I have tried to identify where they are used in the 6309/6. The first main area of use, in pretty much all jewelled watches, is the Escapement and balance. Let me repeat the numbers: "[...] we hear of 6309s being used daily for 20 years without a service..[.].. almost 4 thousand million beats." The 6306 has replaced an escapement hole jewel with a hole-and-cap (2 jewels) giving improved oiling and potentially a slight increase in performance. Less important from a performance point of view are the Gear Train jewels, increased from 5 to 8 in the 6306 by upping the third wheel to a full complement of 2 jewels (replacing a bushing) and adding a cap to one of them) and replacing the fourth wheel bush with a jewel.
For kicks, I wore both the 6306 and the 6309 for the last week, and recorded their timings. Actually, I had started with recording the 6309's time a few days earlier:
Table 4: Results of 6309 timing study.
Table 5: Results of 6306 timing study.
Table 6: Summary of 6306/6309 timing study.
Of course, rates and amplitudes depend on the condition of each watch. The 6309 had some kid of horological hiccup over the weekend, losing a couple of minutes, but seemed to recover. I stopped the test today and will repeat it next week with each watch on the winder for a week at a time.
So there we have a comparison of the 6309 vs 6306 third generation Seiko Diver watches. So similar yet so different. In time, this infatuation for the 6309 divers will pass. Just not for me...
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Harry, Denmark
