The Doppel chrono (reference 3713) is 42mm in diameter and 16mm thick. It has a complicated split-seconds mechanism (an additional second hand) operated by the 10 o'clock pusher.
The very similar looking ref 3706 is 39mm in diameter. This is a normal chronograph (sans the extra sec hand). Both are based on Vajoux 7750.
In the size department, the Doppel was ahead of its time. I remember trying on both in the 90's. The 3713 seemed ridiculously big. I bought the normal-sized 3706.
The watch scene is of course different today. The 3706 now appears to be on the small side while the Dopple looks normal. Strange, how we tune our eyes to new standards.
KT