Alexandre Kossack was lucky to get his hands on this beautiful UN chronograph:
It is a UN ref. no. 536-22, 18 pink gold.
Produced it was in the very first years after Rolf Schnyder took over the company in 1983. It was a difficult time then for the small company, and Rolf Schnyder tried to build up a reputation of fine watchmaking as quickly as possible. Part of that strategy was the use of old and heavily refined chronograph movements in timeless designed watches. Besides the rare rattrapante chronos with Venus movements, there was also a very small series of this attractive full-calendar chronograph, using a Valjoux 88 movement:
According to Ulysse Nardin, less than 50 pieces were made in pink gold, the whole series not exceeding 100 pieces. Later, UN offered a similarly nice chronograph, equipped with a Lémania movement with full calendar complication. This one could be found at some dealers still some years ago.