[Bill Hammack], aka the [EngineerGuy] is at it again, this time explaining how retractable ballpoint pens work. In this excellent video, he describes the simple (but remarkably sophisticated) ...

One of the greatest things ever invented to annoy teachers and help you day-dream at work is undoubtedly the clicky pen. Of course a ‘clicky pen’ is actually called a ‘retractable pen’, and they have ...