The wrist watch revolution started when so-called trench watches became popular with soldiers during WW1. Initially, these were basically small pocket watch movements strapped to the wrist, and this Tavannes example, with a porcelian dial and hinged caseback, certainly fits that bill. I wish I knew a bit more about this watch - the movement is unfortunately unmarked - but I treasure it as the real “granddaddy” of my wristwatch collection.