Texas Instruments SR-10 (1973)

 Math classes were never the same after the introduction of TI's handheld calculators in the early 1970s. The $150 SR-10 debuted in 1973 and was the first affordable handheld to calculate reciprocals, square roots, and other slide-rule functions. The $170 SR-50 followed in 1974, adding trigonometric functions and a very cool 14-character LED display. The devices became so ubiquitous that math whizzes at the time were identified by the simple sobriquet "TIs."