The “Seikomatic 5” 6100 series was a family of mechanical watch movements from Seiko in the 1960's and 1970's.

Produced from 1967 through 1974, the 6100 family was used in many high-end Seiko watches. It was available in both regular 21,600 A/h and high-beat 36,000 versions and both manual winding and automatic versions.

The Hi-Beat 61GS models, introduced in 1968, upstaged the slower 62GS models. That movement was retired in 1969, with the 6100 becoming the high-end Grand Seiko movement. But producing these movements was highly labor-intensive, so Seiko began mechanizing the next year. The 5600 calibre family quickly proved itself for reliability and quartz movements boasted better accuracy, leading to the demise of the 6100 by 1974.

Seiko “resurrected” the 6159A movement in 1975, creating the 6159B for their 600M diver. There is little parts interchange between this later movement and earlier members of the family. It features larger pins to attach the heavier hands of the diver, along with different balance cock and regulating pins similar to the Seiko 4S24.

<table class="html"> <tr> <th>Winding</th><th>Speed</th><th>Model</th><th>Year</th><th>Notes</th> </tr> <tr> <td rowspan=3>Manual</td><td rowspan=13>21600</td><td>61A</td><td>1968</td><td></td> </tr> <tr> <td>6102A</td><td></td><td>Date</td> </tr> <tr> <td>6110A</td><td>1971</td><td>Railroad Watch</td> </tr> <tr> <td rowspan=19>Automatic</td><td>6105A</td><td>1968</td><td>Quickset date</td> </tr> <tr> <td>6105B</td><td></td><td>Quickset date, hacking</td> </tr> <tr> <td>6106A, 6106B, 6106C</td><td>1967</td><td>Day, date, hacking</td> </tr> <tr> <td>6109A</td><td></td><td>Day, date, small rotor</td> </tr> <tr> <td>6117A</td><td>1968</td><td>Quickset date, GMT 24 hour</td> </tr> <tr> <td>6117B</td><td></td><td>Quickset date, GMT 24 hour, hacking</td> </tr> <tr> <td>6118A</td><td></td><td>Quickset date</td> </tr> <tr> <td>6119A, 6119B, 6119C</td><td>1970</td><td>Day, date</td> </tr> <tr> <td><a href="https://www.watch-wiki.net/doku.php?id=seiko_6139">6138A, 6138B</a></td><td>1970</td><td>Chronograph, hour counter, quickset day and date</td> </tr> <tr> <td><a href="https://www.watch-wiki.net/doku.php?id=seiko_6139">6139A, 6139B</a></td><td>1968</td><td>Chronograph, hour counter, quickset day and date</td> </tr> <tr> <td rowspan=9>36000</td><td>6145A</td><td>1968</td><td>Date, Grand Seiko</td> </tr> <tr> <td>6146A</td><td>1968</td><td>Day, date, Grand Seiko</td> </tr> <tr> <td>6155A</td><td>1971</td><td>Date, Grand Seiko Special</td> </tr> <tr> <td>6156A</td><td>1970</td><td>Day, date, Grand Seiko Special</td> </tr> <tr> <td>6159A</td><td>1967</td><td>Quickset date, Diver 300</td> </tr> <tr> <td>6159B</td><td>1975</td><td>Quickset date, hacking, Diver 600</td> </tr> <tr> <td>6185A</td><td>1969</td><td>Grand Seiko Veri Fine Adjusted</td> </tr> <tr> <td>6185B</td><td></td><td>Grand Seiko Veri Fine Adjusted, hacking</td> </tr> <tr> <td>6186A</td><td>1972</td><td>Day, date, Unruhstop, Grand Seiko Veri Fine Adjusted</td> </tr></table>

• Seiko 6139

• The History of Grand Seiko Hi-Beat Movements: Seiko's Affinity to Hi-Beat Movement -- Part One