Recently, I was conversing with a couple of 20-somethings at my fitness club - one was earning an MBA at night in addition to his daytime job at an engineering company.
I mentioned I used a slide rule in my high school Chemistry & Physics classes...and they both were absolutely clueless.
I knew around 1974, when the TI SR-50 came out that the slide rule was obsolete. I knew around 1990 when Excel was on every PC that the calculator was obsolete.