: this is probably a well asked question but how
: come the Micro-rotor chrono movements,
: CAl.11/12/15 are not used now. As it seems
: that the val. 7750 and the el Primero have
: the market.

A couple of reasons...

First off in essance the Micro-Rotor movements (and you forgot the C, 14 and c.11GMT's) are "piggy-backed" module chronographs, which traditionally are seen as less pure or desirable than "clean-sheet" automatic chronographs.

Secondly, the nature of the "module's" that are mated to form a micro-rotor: A Dubois-Depraz chronograph module grafted to a Buren micro-rotor non-chronograph movement isn't exactly an inspiring lineage in the eyes of many watch afficianos.

Thirdly, most people prefer 3-Register (Small second, Hour, Minute) chronograph, and the 2-Register format of the Micro-Rotor's force a decision to be made at the point of purchase, which are you going to sacrifice? The Small Seconds and not be able to tell at a glance if the watch is running? Or the Hour Register and not be able to time for longer than 30-Minutes or an hour. (I call a chronograph without an hour register "half a chronograph" because that's how useful I feel it is. So, of the first three Automatic Chronographs that finished in a dead heat in the race to market, the Micro-Rotor and the Seiko aren't as desirable as the El-Primero.

Fourthly, in the El-Primero, the Valjoux 7750 family, and the Lemania 134x and 5100 movements, all feature a full rotor at the back of the movement, unlike the Micro-Rotor c.11-15 movments. Most people like having a big full rotor at the back of the movement in clear view when the caseback is removed, not a micro movement buried under a chronograph plate or module.

Now having said all of that, I own probably over half a dozen of the micro-rotor movements from Heuer, Hamilton, Bulova, and Chronosport, and with the exception of the Heuer Calculator that I bought off of eBay that looked like it had never been serviced, they have all been good and accurate timkeeper's and run reliabily.

The Zenith, Valjoux and Lemania movements won the battle because they were preferred by most of the chronograph buying public.

-- Chuck