Lots of things, but for one, I’ll mention calculators… especially if you’re in finance or engineering disciplines. They’re built to last and many people continue to use them for many years after college.
The HP 12c financial calculator is HP’s longest and best-selling product, in continual production since its introduction in 1981 [ source ].
For engineering, the HP 48sx 48g 48g II and 50g programmable graphing calculators have been the gold standard for as long as they’ve been in production.
In my opinion, HP is responsible for mainstreaming the use of Reverse Polish Notation in handheld calculators. Once you go RPN, baby, you never go back.
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Dedicated calculator devices are likely on the decline what with the increasingly popularity of mobile computing platforms, like iOS and Android.
HP is ready for that, having released iOS apps for several of their classic calculators already.