Responsiveness

Open up the viz in full screen on your desktop. Then shrink down the width of your browser window and watch the viz NOT getting smaller as the dashboard has got a fixed size of 1400x800. Once the page has less than 600 pixels available the JavaScript code will request the mobile layout of the very same viz. The same happens if you open it up on a mobile device. More infos about how Tableau Server/Online chooses between which viz to render can be found HERE.