So my fancy new 1940s machining book includes a section on how to use a slide rule. Now my book collection does extend to cover things like seven figure mathematical tables, which I do actually use from time to time. Equally learning how calculators operate underneath it all with the log tables and what have you was one of the more interesting parts of maths/computing for me. However despite all that I have never seen a slide rule in the flesh and have (had?) no idea how one works. Maybe it is more of an American thing and the abacus was the method of choice here, I have certainly not heard any old timers mention them in the UK. Either way general thread idea. Find a skill, basic or related to what you already know, that is considered outdated in the modern world and learn it. Then share what it is and possibly something amusing or interesting you did with it. I will also accept things like learning an "old school" trick on a skateboard or something.