If you look closely at large 24 hour chrono register at 9 under the skeletonized hour hand is an inner blasted matte gray center wheel with a thin white line which is the running seconds. The running seconds wheel is centered perfectly within the outer hours track and on the same plane with minimal gap to the outer ring and the skeletonized hour hand means the running seconds is never obscured from view. A separate seconds hands probably would have been easier but added more stack height, the disc is perhaps the more elegant solution. Really thoughtfully done with no expense spared.
If you look at some of Nicolas' pics of the blue one he had you can just see the double rubber bumpers on the left side of the case. Not only do those protect the polished sides of the case but they are mounted to a titanium slider switch. Simply slide down to hack the movement, slide back up again to start. There's a tactile detent in the sliding action so it's easy to manipulate but you can feel confident it won't move by accident. JLC thought of everything!
It's these kinds of details on the Extreme Lab 2 which are not always obvious just by looking at it. Once you live with it for a while you start to appreciate all the tiny details that JLC considered and the way they were implemented with equal thought to visual and mechanical design. Off the cuff the 700 or so parts required to make the Extreme Lab 2 might sound lazy to some, complexity for a lack of ingenuity of design or complexity for complexity's sake, but IMHO this represents JLC's focus to deliver the best possible experience and having the engineering and innovation capabilities to deliver that.