It's got a smooth-iron interior case to protect against magnetic fields along with a double chronograph, aka a break up-second chronograph, a unusual complication that moments two events independently. Lots of Montblanc’s watches are influenced by Minerva pocket watches through the 19th century and the start in the twentieth century. https://sethskyzw.newbigblog.com/38657115/about-mens-watches-under-1000