In my trade school, we had this class devoted exclusively to calculating things fast in memory. The exam consisted of running a bunch of calculations as fast as

In my trade school, we had this class devoted exclusively to calculating things fast in memory. The exam consisted of running a bunch of calculations as fast as possible without writing down anything other than answer. It is interesting that you can learn to calculate a lot of useful stuff in memory and there is a lot of tricks and you can get quite proficient at it after one semester of classes and some training. But once I left this school it was completely unusable skill. It sort of helps me estimate things, a little bit? I guess? But I also carry a phone with me at all times and I have a powerful calculator on my desk just within reach. A skill that is not being used deteriorates, and now I can no longer multiply 5 digit numbers in memory and I use calculator for anything that involves more than 3 digits. And I don't feel like I lost anything. There are so many useful skills to learn. If you want to spend time, learn something else that is more useful. And if you don't want to learn something useful learn something that gives you joy or impresses people.