Just a simple question, why on some Seiko diver watches, the lume bob on the sweep seconds hand is on the opposite end of the pointer?
I answered this question a couple of times in another forum.
The early generation 150M Seiko divers from the late 1960's to 1970's all had automatic movements (Cal. 6217M, Cal. 6159, Cal. 6105, Cal. 6306/9, etc.). In these watches (I believe) all the second hand were equipped with lume "lollipop" on the front tip. This is similar to what you see in most other watches (whether swiss or japanese).
Then Seiko introduced its first (perhaps the world's first also) quartz diver in the late 1970's / 1980's using the Cal. 7548 (non-shrouded diver) and the Cal. 7549 (shrouded / tuna divers). As we all know, the movement of the second hand in a quartz watch starts and stops suddenly throughout its operating life. The stress caused to the quartz movement's gear train is different from that experienced in a mechanical watch.
In tandem with the use of these quartz calibers, the lumed "lollipop" migrated to the rear end of the second hand. Some people called it the "wrong end", but mechanically I was made to understand it was for the purpose of
balancing the mass distribution of the second hand so that the centre of gravity is as close as possible to the rotating axis. This contributes to reducing angular stress and impact on the quartz movement gear trains every time the second hand suddenly starts and stops.
The Seiko divers with Cal 7002 / 7005 in the late 1980's / 1990's were
probably the last automatic seiko divers with the lumed "lollipop" at the front end of the second hand. You will see the second hands in many later seiko divers (in the 1990's and 2000's) with automatic calibers (Cal. 7S26 and 7S36 mostly) also having the lumed "lollipop" but at the rear end like its quartz variants. For example, the SKX007 and SKX009. The second hand in automatic diver moves in sweeping motion, so the stress and impact issue seen in the quartz calibers is not as critical. It can therefore carry both style of second hand (front or rear lumed "lollipop"). IMHO, for these automatic watches, Seiko chose to place the lumed lollipop at the rear end of the second hand for design purposes only and nothing more.
Likewise, Seiko diver movements deriving from quartz technology (for example, the kinetic and solar which came out in the 1990's/2000's) also used the same second hand design (lumed lollipop at the rear end). I am not 100% sure why the same design is used in the free moving Spring Drive diver but I remember reading the reason was to keep low braking force in the tri-synchro regulator mechanism, though I am not 100% convinced.
There are many variants of second hand design to counter the mass distribution problem (in both automatic and quartz watches) so the above is just a very rough guide. Also bear in mind that many seiko watches were modded so they may not carry the original factory second hand.
Hope the above helps.
