HP calculators aren’t for everyone, but many engineers wouldn’t use anything else. The Museum of HP Calculators has lots of interesting information. Of particular interest is the HP-01 which was the first calculator watch released in 1977. You can find them listed on eBay today for thousands of dollars.

If you are a fan of HP Calculators, I recommend you check out HPCalc.org where you can download emulators for your PC or phone.