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The progress of technology is pretty amazing when you think about it. The HP-35 was the first hand-held calculator which has trigonometric and exponential functions. Today there are dozens of apps you can get for free on your smartphone which does much more than this simple calculator, and costs less. The $395 price tag of 1973 would be about $2,500 in today's dollars.

Before the introduction of hand-held calculators people had to use slide-rules for most complex calculations. The HP-35 wa...