Both [SevenZeroOneSix] and [SevenZeroOneSeven] movements have the column wheel/vertical clutch chronograph mechanism found in earlier Seiko chronographs (like the [SixOneThreeEight] and [SixOneThreeNine]) but feature a 12-hour counter on the same subdial as the 30-minute counter. The [SevenZeroOneSix] and [SevenZeroOneSeven] even has a flyback feature which is incredibly useful for this type of watch. Being that it has no sweep second hand (only the chrono seconds) and that the vertical clutch mechanism does not cause any extra wear on the movement to leave the chronograph running all the time (well, minimal extra wear anyway), its handy to leave the chrono running and simply use the flyback feature when you want to time something (a one button start as opposed to a three button start if you had no flyback but left the chronograph running).
The [SevenZeroOneSix] is essentially an 'extension' of Seiko's original auto-winding chronograph calibre, the [SixOneThreeNine] (which only had a 30-min minute counter @ 6 o'clock). The [SixOneThreeNine] tied with 2 Swiss ventures for '1st to market' for an auto-winding chrono calibre in 1969. The [SixOneThreeEight] (with a separate 12-hour counter) came out in 1970, and the [SevenZeroOneSix] was produced from 1972-77. The Swiss consortium of Breitling, Buren-Hamilton, Heuer-Leonidas, and Dubois-Depraz came out with the famous Cal. 11 'Left-handed' Chronomat, while Zenith-Movado came out with it's so-called 'El Primero' the 3019-PHC. The Cal. 11 only lasted in the market about 3 years, due to various problems, but the Seiko [SixOneThreeNine] lasted until 1979 in production, a rather impressive comparison.
