Hi Just thought I would share this, just back form a watch show and picked up a great IWC Doppel split second chronograph, beautiful watch.

movement is based on the 7750 but greatly enhanced from base and split second added.

It was sold as just been serviced by his "master watchmaker in Austin" (isn't every watch sold so) was hard to check over in a quick deal at show, once I got home was late, next morning it had stopped, so took it apart.
Stopped due to simple hand clash of sub second dial to HH, the 12hr chrono would not reset to zero he must have ran it to zero and stopped chrono to make it look correct for show, once apart I seen the problem his "master watchmaker" had put the reset parts in wrong way around and would never work, also the day date wheel was out of sync so fixed it all and now running great, but buyers beware at shows, I can dig myself out of a hold thankfully :-)

There was another came along had a beautiful IWC De Vinci 18K perpetual calendar, he wanted to trade for a couple of mine, I really wanted it so bad, again same story setting books at home, just been serviced.
First thing I seen was the year set at 2006, having just been serviced, why? I advanced the hands no date update, went to quick set no date jump, let alone anyway to set all the rest without book.

Being a very complicated watch no doubt he found out how much to fix if he could find someone to do it, and trying to dump it at the show.

I read later if you move hands backwards on these to change dates it tears them up! OUCH $$$

here the note I found
Although I never added the Da Vinci to my collection, the Ref. 3750 shown above (the rattrapante version was approximately S$19,000 in 1995 and too expensive for me to consider in those days. I don’t remember the price of the 3750, but it was probably about S$12,000). For one reason or another it eluded ownership and remained in the periphery of the watches I wanted.
It was an important watch in several respects. The visual language as expressed by Hano Burtscher’s design is strong. The round case, with articulating lugs, which were separate but part of the case was inspired in part by Leonardo Da Vinci’s Codex Atlanticus. The circle, one of Leonardo da Vinci’s favourite geometrical figures, determined the round shape of the watch case with its four inner sub-dials and two semicircular push-buttons.
The dial design was mandated by the Kurt Klaus design of the perpetual calendar plate which went over the Valjoux 7750 base chronograph movement. The Klaus design was ground breaking for it was one of the first to dispense with the use of pin pushers to adjust the perpetual calendar display. The entire calendar can be set by using only the crown. However, the adjustments can only be made for the calendar going forward, and the watch came with a warning that the mechanism will break if the user adjusted the calendar backwards.
Further, the perpetual calendar was a modular design, meaning that it could be fixed on any movement as a base, from time only to the chronograph. It also showed the year in four digits, a special gear reduction is needed as the first digit of the display only moves about 1.5 mm every 1000 years. Impressive!