1976 was about the time that Commodore made scientific calculators cheap (under $100). Around that time, I remember a Faber-Castell slide rule (a typical engineering-grade device with fine engravings and a cursor that was actually perpendicular to the rule) costing about $30 - and that still left you with three-and-a-bit significant figures, an adding machine for sums and the need to use trig tables. That's pretty much when the student market went away, and anyone who was using alide rules and calculators to make money had little trouble justifying an HP or a TI.