I have always thought that the UI of the 5980 is particularly successful. The readability is excellent and the dial is uncluttered. I like the subsidiary dial with the 60-minute and the 12-hour monocounter. What do you think? ...
I have always assumed Patek designed the chronograph register(s) of the CH 28-520 movement to fit well with additional complications. By having the single sub-dial, there is plenty of room on the dial for things such as calendar displays, etc.