profile view close-up sequence showing the hand of a middle-aged man with a watch writing illegibly with chalk on an old-fashioned blackboard in a room lit with natural light, uk. - blackboard 個影片檔及 b 捲影像00:18
sequence showing three close-up shots of a middle-aged man drawing the axis of a simple graph with chalk onto an old-fashioned, free-standing blackboard, uk. - blackboard 個影片檔及 b 捲影像00:20