So I saw the photo below showing a bunch of old calculators:
and it made me remember the one that got me through all my electrical engineering courses, mainly because I could secretly type formulas into it in case I couldn’t remember them for the exam. The classic HP41CV:
Hard to believe that at the time they cost $325. I could get an entire laptop for that now, especially when adjusted from mid-1980s dollars.
Wayne's Whirled 
I was in my first circuits class in ’71 when the first HP scientific calculator came out, the HP-35 (http://en.wikipedia.org/wiki/HP-35) selling for about $400. All the cool kids had them stuffed in their shirt pocket, but us regular folks still had to use sliderules ($400 was a LOT of $$ back then). A couple years later I was able to afford TI’s counter to the HP-35, the $170 SR-50 (http://en.wikipedia.org/wiki/TI_SR-50). Used all 10 digits of floating point precision in my nuclear engineering class. I still have my Pickett N3 rule (http://www.sliderules.info/collection/10inch/030/1037-pickett-n3-es.htm), though I have absolutely NO idea how do anything but multiply any more. Nostalgia for sure.
I remember that everyone in my physics class had the exact same Texas Instruments calculator. What I really remember is that distinctive clicking sound that went on during our tests.