I've looked into this before. I gave up. It had little utility, even in daily life because humans make mistakes regularly. I have a mathematics degree so it's not like I can't do it but I quote one of my tutors "better to use a calculator than fuck it up and find out a page of working later". So I use a calculator.

Smart. This is kin to a circus trick, a thing that impresses people but in reality has little to no actual value. It could be useful in some settings though, like at a party, interview or impressing an investor or even a potential partner.