Calculators went from something that was really expensive to something that was relatively affordable over a very short period of time. In about 1974, a 5-function TI was about $100 (in 1975 currency). By the next year a full scientific TI calculator wasn't much more and no one, at least in engineering school, was still using a slide rule though I brought one to exams as a a backup. By a couple years later, I was able to buy a discontinued HP calculator for about the same.