The SI system has been published 1960, but many incorrigible physicists (particularly the theoretical ones, shame on them) still use the CGS system. Manually converting expressions from one system to the other is one of the most dreadful (aka boring) thing in a physicist's life. As a PhD student, I did exactly that day in, day out. As a postdoc, I discovered ye olde units. Just like graph, this wonderful tool is essentially unknown to modern Linux users, but very useful not only for physicists. Or can you tell me right away (and with reasonable accuracy!) what's a 112 Fahrenheit in Celsius, a 25 stones in kg, or 12 yards, 6 foot 8 inch in cm? Voilà: