(Sưu tầm tin tức) According to The Seiko Book, commercial production of the cal. 5606, based on the 56 caliber stream, started in 1968. The 5606 had a 21600 beat rate, offered quick set day and date, hand winding from the crown, and the ability to precisely set the seconds though a hacking lever. The 56 stream seams to have been developed between two other caliber streams, the 51(starting in 1967), and the 52 (starting in 1970). When the 51 was developed, it had a thickness of 4.9mm. The Cal. 56 steam had a reduced thickness of 4.3mm, and the 52 stream further reduced the movements thickness to 3.9mm. In this continuing effort to reduce the thickness of its mid to high grade movements, many novel design elements were incorporated into the 5606. The following essay is designed to highlight some of these features and design elements, and to allow the reader to appreciate what Seiko was doing at the time. Below, we see the top plate, or back of the movement, as it is after being decased from a one piece case. In the photo above, we can see a high degree of consideration in the movement. From the colimaconnage on the winding weight, crown, and ratchet wheels. The high polished angles on the plates. The cap jewels on the escape and third wheels, to the micro regulator used on the balance cock, this movement is no slouch in the visual appreciation department. With the winding weight (commonly referred to as the rotor) removed, we can see the major deciding design factor in the reduction of thickness in these three movements (51,56,52). Placing (integrating) the autowinding train wheels at the same level of the time keeping train was the key to reducing the thickness of the automatic watch. With the autowinding and time trains under the same bridge, valuable real-estate was removed from the top plate. Prior to this integration, most automatic watches relied on a separate autowinding system that was attached to an already existing hand winding caliber. This system of adding a autowind train to an existing caliber can be best remembered by the Rolex Bubble Back, a term that was used to describe the fact that if you wanted an automatic, you paid for it in the thickness of the watch. Seiko was a major developer of this "integrated" thinking.