I believe this was Seiko's first chronograph made in 1964. It was made for that year only as Tokyo was hosting the summer games and Seiko wanted to show they were a serious watchmaker. There are a few iterations of this reference 5719, all very nice but my personal favorite happens to be this iteration. Thanks for looking!
All of my Seikos are kept at home (while many others slumber in a safe deposit box), but unusually, this one hasn't had any wrist time in quite a while. It'll be on my wrist thru the weekend.